Resin sheet

ABSTRACT

Resin sheets which includes a support and a resin composition layer in contact on the support, and which are characterized in that an extracted water conductivity A of a cured product of the resin composition layer when extracted at 120° C. for 20 hours is 50 μS/cm or less and an extracted water conductivity B of the cured product of the resin composition layer when extracted at 160° C. for 20 hours is 200 μS/cm or less, can provide a thin insulating layer having excellent insulating properties.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2016-066204, filed on Mar. 29, 2016, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to resin sheets. The present inventionalso relates to printed wiring boards and semiconductor devices eachincluding a cured product of resin composition layer of such a resinsheet.

Discussion of the Background

In recent years, in order to achieve downsizing of electronic devices,further thinning of printed wiring boards has been advanced and thus thethickness of internal layer substrates and insulating layers have tendedto be thinner. As a technique of thinning of internal layer substratesand insulating layers, for example, a resin composition for forming athin film described in JP-A-2014-152309, which is incorporated herein byreference in its entirety, has been known.

However, there remains a need for improved printed wiring boards.

SUMMARY OF THE INVENTION

In JP-A-2014-152309, the present inventors have found that when a thinfilm is used for an insulating layer, the roughness tends to increaseand the peeling strength tends to decrease. In order to solve theseproblems, the present inventors have suggested adding a thermoplasticresin in a predetermined amount. In the literature, however, theinsulating property when the insulating layer is made to be thin(hereinafter, may also be referred to as “thin film insulatingproperty”) has not been studied at all.

When the insulating layer is a thin film, retaining the insulatingproperty becomes difficult compared with conventional ones, becausecontact of inorganic filler particles with each other causes electriccurrent to easily flow through their interfaces, an increase inelectrostatic capacity due to the thinner insulating layer easily causesshort circuit, and the like.

Accordingly, it is one object of the present invention to provide novelresin sheets that can provide a thin insulating layer having anexcellent insulating property.

It is another object of the present invention to provide novel printedwiring boards and semiconductor devices each including a cured productof resin composition layer of such a resin sheet.

These and other objects, which will become apparent during the followingdetailed description, have been achieved by the inventors' discoverythat a resin sheet including a support and a resin composition layerbeing in contact on the support, in which the cured product of the resincomposition layer satisfies at least one of the predetermined extractedwater conductivity and the predetermined tensile breaking strengthratio, can provide an insulating layer having excellent insulatingproperty (excellent thin film insulating property) even when thethickness of the insulating layer is thin. More specifically, thepresent inventors have found that the insulating layer having excellentthin film insulating property can be provided by lowering the extractedwater conductivity of the cured product when extracted at hightemperature or reducing the deterioration in the tensile breakingstrength when the cured product is placed under a high-temperature andhigh-humidity environment.

Specifically, the present invention provides the following embodiments:

(1) A resin sheet comprising:

a support; and

a resin composition layer being in contact on the support, wherein

an extracted water conductivity A of a cured product of the resincomposition layer when extracted at 120° C. for 20 hours is 50 μS/cm orless and an extracted water conductivity B of the cured product of theresin composition layer when extracted at 160° C. for 20 hours is 200μS/cm or less.

(2) The resin sheet according to (1), wherein a glass transitiontemperature of the cured product of the resin composition layer is 160°C. or more.

(3) A resin sheet comprising:

a support; and

a resin composition layer being in contact on the support, wherein

a ratio (B/A) of a tensile breaking strength B of a 10 μm thicknesscured product of the resin composition layer after a HAST test to atensile breaking strength A of a 10 μm thickness cured product of theresin composition layer is 0.65 or more and 1 or less.

(4) The resin sheet according to (3), wherein the tensile breakingstrength B is 50 MPa or more.

(5) The resin sheet according to any one of (1) to (4), wherein theresin composition layer has a thickness of 15 μm or less.

(6) The resin sheet according to any one of (1) to (5), wherein theresin composition layer has a lowest melt viscosity of 1000 poise ormore.

(7) The resin sheet according to any one of (1) to (6), wherein theresin composition layer contains an epoxy resin and a curing agent.

(8) The resin sheet according to any one of (1) to (7), wherein theresin composition layer contains an inorganic filler, and the inorganicfiller has a content of 50% by mass or more when a nonvolatile componentin the resin composition layer is determined to be 100% by mass.

(9) The resin sheet according to (8), wherein the inorganic filler hasan average particle diameter of 0.05 μm to 0.35 μm.

(10) The resin sheet according to (8) or (9), wherein a product of aspecific surface area (m²/g) and a true density (g/cm³) of the inorganicfiller is 0.1 to 77.

(11) The resin sheet according to any one of (1) to (10), wherein theresin sheet is used for forming an insulating layer of a printed wiringboard.

(12) The resin sheet according to any one of (1) to (11), wherein theresin sheet is used for forming an insulating layer of a printed wiringboard comprising a first conductive layer, a second conductive layer,and the insulating layer that insulates the first conductive layer fromthe second conductive layer and has a thickness of 6 μm or less betweenthe first conductive layer and the second conductive layer.

(13) A printed wiring board comprising:

a first conductive layer,

a second conductive layer, and

an insulating layer that insulates the first conductive layer from thesecond conductive layer and has a thickness of 6 μm or less between thefirst conductive layer and the second conductive layer, wherein

the insulating layer is the cured product of the resin composition layerof the resin sheet according to any one of (1) to (12).

(14) A semiconductor device, comprising the printed wiring boardaccording to (13).

Advantageous Effects of Invention

The present invention can provide a resin sheet that can provide a thininsulating layer having an excellent insulating property.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a partial cross-section view schematically illustrating anembodiment of a printed wiring board.

EXPLANATION OF REFERENCE NUMERALS

-   -   5 first conductive layer    -   51 main surface of first conductive layer    -   6 second conductive layer    -   61 main surface of second conductive layer    -   7 insulating layer

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the resin sheet of the present invention, and the printedwiring board and the semiconductor device each including a cured productof resin composition layer of the resin sheet will be described indetail.

The resin sheet of the present invention includes a support and a resincomposition layer being in contact on the support. The present inventionis characterized in that a cured product of the resin composition layersatisfies at least one of the specific extracted water conductivity(Property 1) and the specific tensile breaking strength ratio (Property2) noted below. In Property 2, “tensile breaking strength A of a 10 μmthickness cured product of the resin composition layer” means “tensilebreaking strength A before a HAST test that a cured product of the resincomposition layer exhibits when a thickness thereof is 10 μm.” Also,“tensile breaking strength B of a 10 μm thickness cured product of theresin composition layer after HAST test” means “tensile breakingstrength B after HAST test that a cured product of the resin compositionlayer exhibits when a thickness thereof is 10 μm.” It is noted thatProperty 2 does not limit a thickness of resin composition layer in theresin sheet.

Property 1

An extracted water conductivity A of a cured product of the resincomposition layer when extracted at 120° C. for 20 hours is 50 μS/cm orless and an extracted water conductivity B of a cured product of theresin composition layer when extracted at 160° C. for 20 hours is 200μS/cm or less.

Property 2

A ratio (B/A) of a tensile breaking strength B of a 10 μm thicknesscured product of the resin composition layer after HAST test to atensile breaking strength A of a 10 μm thickness cured product of theresin composition layer is 0.65 or more and 1 or less.

The resin composition layer is formed from resin composition. There willbe firstly described a resin composition for forming the resincomposition layer.

Resin Composition

The resin composition is not particularly limited as long as a curedproduct of resin composition layer formed from the resin compositionsatisfies at least one of Property 1 and Property 2. Examples of theresin composition that provides the cured product satisfying at leastone of Property 1 and Property 2 may include a composition containing acurable resin and a curing agent thereof. As the curable resin, knowncurable resins used for forming the insulating layer of a printed wiringboard may be used. Among them, an epoxy resin is preferable. In oneembodiment, therefore, the resin composition contains (A) an epoxy resinand (B) a curing agent. The resin composition preferably contains (C) aninorganic filler. The resin composition may contain additives such as athermoplastic resin, a curing accelerator, a flame retardant, and anorganic filler, if necessary.

Hereinafter, there will be described (A) the epoxy resin, (B) the curingagent, (C) the inorganic filler and the additives that may be used as amaterial for the resin composition.

(A) Epoxy Resin

Examples of (A) the epoxy resin may include a bisphenol A epoxy typeresin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, abisphenol AF type epoxy resin, a dicyclopentadiene type epoxy resin, atrisphenol type epoxy resin, a naphthol novolac type epoxy resin, aphenol novolac type epoxy resin, a tert-butyl-catechol type epoxy resin,a naphthalene type epoxy resin, a naphthol type epoxy resin, ananthracene type epoxy resin, a glycidylamine type epoxy resin, aglycidyl ester type epoxy resin, a cresol novolac type epoxy resin, abiphenyl type epoxy resin, a linear aliphatic epoxy resin, an epoxyresin having a butadiene structure, an alicyclic epoxy resin, aheterocyclic epoxy resin, a Spiro ring containing epoxy resin, acyclohexane dimethanol type epoxy resin, a naphthylene ether type epoxyresin, a trimethylol type epoxy resin, and a tetraphenylethane typeepoxy resin. These epoxy resin may be used alone or in combination oftwo or more kinds thereof. The component (A) is preferably one or moreselected from the bisphenol A type epoxy resin, the bisphenol F typeepoxy resin, and the biphenyl type epoxy resin.

The epoxy resin preferably contains an epoxy resin having two or moreepoxy groups per molecule. It is preferable that the epoxy resincontains an epoxy resin having two or more epoxy groups per molecule inan amount of at least 50% by mass or more when the nonvolatile componentin the epoxy resin is determined to be 100% by mass. In particular, itis preferable that the epoxy resin contain an epoxy resin that has twoor more epoxy groups per molecule and is liquid at 20° C. (hereinafterreferred to as “liquid epoxy resin”) and an epoxy resin that has threeor more epoxy groups per molecule and is solid at 20° C. (hereinafterreferred to as “solid epoxy resin”). When the liquid epoxy resin and thesolid epoxy resin are used in combination as the epoxy resin, a resincomposition having excellent flexibility can be obtained. Further, therupture strength of cured product of the resin composition is enhanced.In particular, the solid epoxy resin has high heat resistance, allows anextracted water conductivity of a cured product when extracted at hightemperature to be easily lowered, and tends to suppress deterioration ina tensile breaking strength when a cured product is placed underhigh-temperature and high-humidity.

The liquid epoxy resin is preferably a bisphenol A type epoxy resin, abisphenol F type epoxy resin, a bisphenol AF type epoxy resin, anaphthalene type epoxy resin, a glycidyl ester type epoxy resin, aglycidylamine type epoxy resin, a phenol novolac type epoxy resin, analicyclic epoxy resin having an ester skeleton, a cyclohexane dimethanoltype epoxy resin, a glycidylamine type epoxy resin, or an epoxy resinhaving butadiene structure; and more preferably, a glycidylamine typeepoxy resin, a bisphenol A type epoxy resin, a bisphenol F type epoxyresin, a bisphenol AF type epoxy resin, and a naphthalene type epoxyresin. Specific examples of the liquid epoxy resin may include “HP4032”,“HP4032D”, and “HP4032SS” (naphthalene type epoxy resins) available fromDIC Corporation, “828US” and “jER828EL” (bisphenol A type epoxy resins),“jER807” (a bisphenol F type epoxy resin), “jER152” (a phenol novolactype epoxy resin), “YL7760” (a bisphenol AF type epoxy resin) “630” and“630LSD” (glycidylamine type epoxy resins) available from MitsubishiChemical Corporation, “ZX1059” (mixed product of a bisphenol A typeepoxy resin and a bisphenol F type epoxy resin) available from NIPPONSTEEL & SUMIKIN CHEMICAL CO., LTD., “YD-8125G” (a bisphenol A type epoxyresin) available from NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD.,“EX-721” (a glycidyl ester type epoxy resin) available from NagaseChemteX Corporation, “CELLOXIDE 2021P” (an alicyclic epoxy resin havingan ester skeleton), “PB-3600” (an epoxy resin having a butadienestructure) available from Daicel Corporation, “ZX1658” and “ZX1658GS”(liquid 1,4-glycidyl cyclohexane) available from Nippon Steel ChemicalCo., Ltd., and “630LSD” (a glycidylamine type epoxy resin) availablefrom Mitsubishi Chemical Corporation. These resins may be used alone orin combination of two or more kinds thereof.

The solid epoxy resin is preferably a tetrafunctional naphthalene typeepoxy resin, a cresol novolac type epoxy resin, a dicyclopentadiene typeepoxy resin, a trisphenol type epoxy resin, a naphthol type epoxy resin,a biphenyl type epoxy resin, a naphthylene ether type epoxy resin, ananthracene type epoxy resin, a bisphenol A type epoxy resin, or atetraphenyl ethane type epoxy resin; and more preferably atetrafunctional naphthalene type epoxy resin, a naphthol type epoxyresin, or a biphenyl type epoxy resin. Specific examples of the solidepoxy resin may include “HP4032H” (a naphthalene type epoxy resin),“HP-4700” and “HP-4710” (tetrafunctional naphthalene type epoxy resins),“N-690” (a cresol novolac type epoxy resin), “N-695” (a cresol novolactype epoxy resin), “HP-7200”, “HP-72001TH”, and “HP-7200H”(dicyclopentadiene type epoxy resins), “EXA-7311”, “EXA-7311-G3”,“EXA-7311-G4”, “EXA-7311-G4S”, and “HP6000” (naphthylene ether typeepoxy resins) available from DIC Corporation, “EPPN-502H” (a trisphenoltype epoxy resin), “NC7000L” (a naphthol novolac type epoxy resin),“NC3000H”, “NC3000”, “NC3000L”, and “NC3100” (biphenyl type epoxyresins) available from Nippon Kayaku Co., Ltd., “ESN475V” (a naphthalenetype epoxy resin) and “ESN485” (a naphthol novolac type epoxy resin)available from NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD., “YX4000H” and“YL6121” (biphenyl type epoxy resins), “YX4000HK” (a bixylenol typeepoxy resin), and “YX8800” (an anthracene type epoxy resin) availablefrom Mitsubishi Chemical Corporation, “PG-100” and “CG-500” availablefrom Osaka Gas Chemicals Co., Ltd., “YL7800” (a fluorene type epoxyresin) available from Mitsubishi Chemical Corporation, and “jER1010” (asolid bisphenol A type epoxy resin) and “jER1031S” (a tetraphenylethanetype epoxy resin) available from Mitsubishi Chemical Corporation.

As the epoxy resin, high purity resins (for example, resins in which anamount of ionic impurities such as chlorine ions is low) are preferablefrom the viewpoint of allowing an extracted water conductivity of acured product of the resin composition layer to be easily lowered andsuppressing deterioration in a tensile breaking strength when a curedproduct of the resin composition layer is placed under ahigh-temperature and high-humidity environment. Examples of the highpurity epoxy resins may include “828US”, “YL980”, “1750”, and “YL983U”available from Mitsubishi Chemical Corporation, and “YD-8125G”,“YD-825GS”, “ZX-1658GS”, and “YDF-8170G” available from NIPPON STEEL &SUMIKIN CHEMICAL CO., LTD.

As the liquid epoxy resin, an aromatic epoxy resin having two or moreepoxy groups per molecule and being in a liquid state at a temperatureof 20° C. is preferable. As the solid epoxy resin, an aromatic epoxyresin having three or more epoxy groups per molecule and being in asolid state at a temperature of 20° C. is preferable. The aromatic epoxyresin referred in the present invention means an epoxy resin having anaromatic ring structure in the molecule thereof.

When the liquid epoxy resin and the solid epoxy resin are used incombination as the epoxy resin, a mass ratio thereof (liquid epoxyresin:solid epoxy resin) is preferably in a range of 1:0.1 to 1:15. Whenthe mass ratio of the liquid epoxy resin to the solid epoxy resin fallswithin such a range, the following effects can be obtained: i) moderatetackiness can be obtained when the resin composition is used in a resinsheet form; ii) sufficient flexibility can be obtained when the resincomposition is used in a resin sheet form, and as a result,handleability is improved; and iii) a cured product having sufficientrupture strength can be obtained from the resin composition layer. Fromthe viewpoints of the effects i) to iii), the mass ratio of the liquidepoxy resin to the solid epoxy resin (liquid epoxy resin:solid epoxyresin) is more preferably in a range of 1:2.0 to 1:12, and furtherpreferably in a range of 1:3.0 to 1:10.

The content of the epoxy resin in the resin composition is preferably 5%by mass or more, more preferably 9% by mass or more, and furtherpreferably 13% by mass or more from the viewpoint of obtaining theinsulating layer exhibiting excellent tensile breaking strength andinsulation reliability. The upper limit of the content of the epoxyresin is not particularly limited as long as the effects of the presentinvention are exerted, and is preferably 50% by mass or less and morepreferably 40% by mass or less.

In the present invention, the content of each component in the resincomposition is a value when the nonvolatile components in the resincomposition is determined to be 100% by mass, unless otherwisespecified.

The epoxy equivalent weight of the epoxy resin is preferably 50 to5,000, more preferably 50 to 3,000, further preferably 80 to 2,000, andfurther more preferably 110 to 1,000. When the epoxy equivalent weightfalls within such a range, the crosslinking density of the cured productof the resin composition layer becomes sufficient and an insulatinglayer having small surface roughness can be obtained. The epoxyequivalent weight can be measured in accordance with JIS K 7236. Theepoxy equivalent weight means the mass of a resin containing oneequivalent of epoxy group.

The weight average molecular weight of the epoxy resin is preferably 100to 5,000, more preferably 250 to 3,000, and further preferably 400 to1,500. Here, the weight average molecular weight of the epoxy resin is apolystyrene-equivalent weight average molecular weight measured by a gelpermeation chromatography (GPC) method.

(B) Curing Agent

The curing agent is not particularly limited as long as it has afunction of curing the epoxy resin. Examples thereof may include aphenol-based curing agent, a naphthol-based curing agent, an activeester-based curing agent, a benzoxazine-based curing agent, a cyanateester-based curing agent, and a carbodiimide-based curing agent. Thecuring agents may be used alone or in combination of two or more kindsthereof.

As the phenol-based curing agent and the naphthol-based curing agent, aphenol-based curing agent having a novolac structure or a naphthol-basedcuring agent having a novolac structure is preferable from the viewpointof heat resistance and water resistance. A nitrogen-containingphenol-based curing agent is preferable and a triazineskeleton-containing phenol-based curing agent is more preferable fromthe viewpoint of adhesion to the conductive layer. Among them, atriazine skeleton-containing phenol novolac curing agent is preferablefrom the viewpoint of highly satisfying heat resistance, waterresistance, and adhesion to a conductive layer.

Specific examples of the phenol-based curing agent and thenaphthol-based curing agent may include “MEH-7700”, “MEH-7810”, and“MEH-7851” available from Meiwa Plastic Industries, Ltd., “NHN”,” “CBN”,and “GPH” available from Nippon Kayaku Co., Ltd., “SN170”, “SN180”,“SN190”, “SN475”, “SN485”, “SN495”, “SN-495V”, “SN375”, and “SN395”available from NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD., and “TD-2090”,“LA-7052”, “LA-7054”, “LA-1356”, “LA-3018-50P”, and “EXB-9500” availablefrom DIC Corporation.

The active ester-based curing agent is not particularly limited, and acompound having two or more highly reactive ester groups per molecule,such as phenol esters, thiophenol esters, N-hydroxyamine esters, andesters of heterocyclic hydroxy compounds, is generally preferably used.It is preferable that the active ester-based curing agent be an activeester-based curing agent obtained by a condensation reaction of acarboxylic acid compound and/or a thiocarboxylic acid compound with ahydroxy compound and/or a thiol compound. In order to especially enhancethe heat resistance, an active ester-based curing agent obtained from acarboxylic acid compound and a hydroxy compound is preferable, and anactive ester-based curing agent obtained from a carboxylic acid compoundand a phenol compound and/or a naphthol compound is more preferable.Examples of the carboxylic acid compound may include benzoic acid,acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid,isophthalic acid, terephthalic acid, and pyromellitic acid. Examples ofthe phenol compound or naphthol compound may include hydroquinone,resorcin, bisphenol A, bisphenol F, bisphenol S, phenolphthalin,methylated bisphenol A, methylated bisphenol F, methylated bisphenol S,phenol, o-cresol, m-cresol, p-cresol, catechol, α-naphthol, β-naphthol,1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene,2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone,tetrahydroxybenzophenone, phloroglucin, benzenetriol, adicyclopentadiene type diphenol compound, and phenol novolac. The“dicyclopentadiene type diphenol compound” herein is a diphenol compoundobtained by condensation of one dicyclopentadiene molecule with twophenol molecules.

Specifically, an active ester compound containing a dicyclopentadienetype diphenol structure, an active ester compound containing anaphthalene structure, an active ester compound containing an acetylatedcompound of phenol novolac, and an active ester compound containing abenzoylated compound of phenol novolac are preferable. Among them, anactive ester compound containing a naphthalene structure and an activeester compound containing a dicyclopentadiene type diphenol structureare more preferable. The “dicyclopentadiene type diphenol structure” isa divalent structural unit of phenylene-dicyclopentylene-phenylene.

Examples of a commercially available product of the active ester-basedcuring agent may include “EXB9451,” “EXB9460,” “EXB9460S,”“HPC-8000-65T,” “HPC-8000H-65TM,” and “EXB-8000L-65TM” as an activeester compound containing a dicyclopentadiene type diphenol structure(available from DIC Corporation), “EXB9416-70BK” as an active estercompound containing a naphthalene structure (available from DICCorporation), “DC808” as an active ester compound containing anacetylated compound of phenol novolac (available from MitsubishiChemical Corporation), “YLH1026” as an active ester compound containinga benzoylated compound of phenol novolac (available from MitsubishiChemical Corporation), “DC808” as an active ester curing agent that isan acetylated compound of phenol novolac (available from MitsubishiChemical Corporation), and “YLH1026,” “YLH1030,” and “YLH1048” as anactive ester curing agent that is a benzoylated compound of phenolnovolac (available from Mitsubishi Chemical Corporation).

Specific examples of the benzoxazine-based curing agent may include“HFB2006M” available from Showa Highpolymer Co., Ltd., and “P-d” and“F-a” available from Shikoku Chemicals Corporation.

Examples of the cyanate ester-based curing agent may include abifunctional cyanate resin such as bisphenol A dicyanate, polyphenolcyanate, oligo(3-methylene-1,5-phenylenecyanate),4,4′-methylenebis(2,6-dimethylphenyl cyanate), 4,4′-ethylidenediphenyldicyanate, hexafluorobisphenol A dicyanate,2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanatephenylmethane),bis(4-cyanate-3,5-dimethylphenyl)methane,1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene,bis(4-cyanatephenyl)thioether, and bis(4-cyanatephenyl)ether; apolyfunctional cyanate resin derived from phenol novolac and cresolnovolac; and a prepolymer in which these cyanate resin are partlytriazinized. Specific examples of the cyanate ester-based curing agentmay include “PT30” and “PT60” (both phenol novolac type polyfunctionalcyanate ester resins), “ULL-950”” (a multifunctional cyanate esterresin), and “BA230” and “BA230S75” (prepolymer in which bisphenol Adicyanate is partly or entirely triazinized to form a trimer) availablefrom Lonza Japan Ltd.

Specific examples of the carbodiimide-based curing agent may include“V-03” and “V-07” available from Nisshinbo Chemical Inc.

The component (B) is preferably one or more selected from a phenol-basedcuring agent, a naphthol-based curing agent, an active ester-basedcuring agent, and a cyanate ester-based curing agent. The curing agentis preferably a curing agent having high heat stability from theviewpoint of allowing an extracted water conductivity of a cured productof the resin composition layer to be lowered and suppressingdeterioration in a tensile breaking strength when a cured product of theresin composition layer is placed under a high-temperature andhigh-humidity environment. Examples of the curing agent having high heatstability may include an active ester-based curing agent, a cyanateester-based curing agent, and a carbodiimide-based curing agent. Thecuring agent is preferably one or more selected from an activeester-based curing agent and a cyanate ester-based curing agent, andfurther preferably an active ester-based curing agent from the viewpointof achieving a high hydrophobic property and allowing an extracted waterconductivity of a cured product of the resin composition layer to belowered and suppressing deterioration a the tensile breaking strengthwhen a cured product of the resin composition layer is placed under ahigh-temperature and high-humidity environment.

The quantitative ratio of the epoxy resin to the curing agent, in termsof a ratio of [the total number of epoxy groups in the epoxy resin]:[thetotal number of reactive groups in the curing agent], is in a range ofpreferably 1:0.01 to 1:2, more preferably 1:0.015 to 1:1.5, and furtherpreferably 1:0.02 to 1:1. Herein, the reactive group in the curing agentis an active hydroxyl group, an active ester group, or the like, andvaries depending on the kind of the curing agent. The total number ofepoxy groups in the epoxy resin is a value obtained by dividing the massof solid content in each epoxy resin by respective epoxy equivalentweights and summing the calculated values for all the epoxy resins. Thetotal number of reactive groups in the curing agent is a value obtainedby dividing the mass of solid content in each curing agent by respectivereactive group equivalent weights and summing the calculated values forall the curing agents. When the quantitative ratio of the epoxy resin tothe curing agent falls within such a range, the heat resistance of thecured product of the resin composition layer is more improved.

In one embodiment, the resin composition contains the epoxy resin andthe curing agent noted above. It is preferable that the resincomposition contain a mixture of the liquid epoxy resin and the solidepoxy resin (the mass ratio of the liquid epoxy resin:the solid epoxyresin is preferably 1:0.1 to 1:15, more preferably 1:0.3 to 1:12, andfurther preferably 1:0.6 to 1:10) as (A) the epoxy resin, and one ormore selected from the group consisting of the phenol-based curingagent, the naphthol-based curing agent, the active ester-based curingagent, and the cyanate ester-based curing agent (preferably one or moreselected from the group consisting of the active ester-based curingagent and the cyanate ester-based curing agent) as (B) the curing agent.

The content of the curing agent in the resin composition is notparticularly limited and is preferably 30% by mass or less, morepreferably 25% by mass or less, and further preferably 20% by mass orless. The lower limit is not particularly limited and is preferably 2%by mass or more.

(C) Inorganic Filler

In one embodiment, the resin composition may contain an inorganicfiller. A material for the inorganic filler is not particularly limited.Examples thereof may include silica, alumina, glass, cordierite, siliconoxide, barium sulfate, barium carbonate, talc, clay, a mica powder, zincoxide, hydrotalcite, boehmite, aluminum hydroxide, magnesium hydroxide,calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride,aluminum nitride, manganese nitride, aluminum borate, strontiumcarbonate, strontium titanate, calcium titanate, magnesium titanate,bismuth titanate, titanium oxide, zirconium oxide, barium titanate,barium zirconate titanate, barium zirconate, calcium zirconate,zirconium phosphate, and zirconium phosphate tungstate. Among them,silica is particularly suitable. Examples of silica may includeamorphous silica, fused silica, crystalline silica, synthetic silica,and hollow silica. As the silica, spherical silica is preferable. Theinorganic fillers may be used alone or in combination of two or morekinds thereof.

The average particle diameter of the inorganic filler is preferably 0.35μm or less, more preferably 0.32 μm or less, further preferably 0.3 vimor less, and further more preferably 0.29 μm or less from the viewpointof highly filling the inorganic filler and improving the thin filminsulating property. The lower limit of the average particle diameter ispreferably 0.05 μm or more, more preferably 0.06 μm or more, and furtherpreferably 0.07 μm or more from the viewpoint of improvingdispersibility in the resin composition layer. Examples of commerciallyavailable products of the inorganic filler having such an averageparticle diameter may include “UFP-30” available from Denka CompanyLimited and “SPH 516-05” available from NIPPON STEEL & SUMIKIN MATERIALSCo., Ltd.

The average particle diameter of the inorganic filler can be measured bya laser diffraction and scattering method on the basis of the Miescattering theory. Specifically, the particle size distribution of theinorganic filler is prepared on the basis of volume, and a mediandiameter thereof can be measured as an average particle diameter using alaser diffraction and scattering particle size distribution measuringdevice. As a measurement sample, a dispersion in which the inorganicfiller is dispersed in methyl ethyl ketone by ultrasonication can bepreferably used. As the laser diffraction and scattering particle sizedistribution measuring device, “SALD-2200” manufactured by ShimadzuCorporation or the like can be used.

The specific surface area of the inorganic filler is preferably 40 m²/gor less, more preferably 37 m²/g or less, and further preferably 33 m²/gor less from the viewpoint of lowering the lowest melt viscosity of theresin composition layer described below. The lower limit of the specificsurface area is preferably 1 m²/g or more, more preferably 5 m²/g ormore, further preferably 10 m²/g or more, or 15 m²/g or more from theviewpoint of maintaining adequate viscoelasticity of the resincomposition layer. The specific surface area can be measured with, forexample, a BET full automatic specific surface area measuring apparatus(Macsorb HM-1210, manufactured by Mountech Co., Ltd.).

The true density of the inorganic filler is preferably 15 g/cm³ or less,more preferably 10 g/cm³ or less, and further preferably 5 g/cm³ or lessfrom the viewpoint of improving dispersibility in the resin compositionlayer. The lower limit of the true density is preferably 1 g/cm³ ormore, more preferably 1.5 g/cm³ or more, and further preferably 2.0g/cm³ or more. The true density can be measured with, for example, MicroUltra-Pycnometer (MUPY-21T, manufactured by Quantachrome InstrumentsJapan G. K.).

The product of the specific surface area (m²/g) of the inorganic fillerand the true density (g/cm³) of the inorganic filler is preferably 0.1to 77, more preferably 26 to 77, further preferably 30 to 70, andfurther more preferably 35 to 70. When the product falls within theabove range, the thin film insulating property can be improved.

From the viewpoint of enhancing the humidity resistance anddispersibility, it is preferable that the inorganic filler issurface-treated with at least one surface treatment agent such as asilane coupling agent, an alkoxysilane compound, an organosilazanecompound, and the like. These surface treatment agents may be oligomers.Examples of the surface treatment agent may include a silane-basedcoupling agent such as an aminosilane-based coupling agent, anepoxysilane-based coupling agent and a mercaptosilane-based couplingagent; an alkoxysilane compound; an organosilazane compound; and atitanate-based coupling agent. Examples of commercially availablesurface treatment agents may include “KBM403”(3-glycidoxypropyltrimethoxysilane), “KBM803”(3-mercaptopropyltrimethoxy), “KBE903” (3-aminopropyltriethoxysilane),“KBM573” (N-phenyl-3-aminopropyltrimethoxysilane), “SZ-31”(hexamethyldisilazane), “KBM103” (phenyltrimethoxysilane), and““KBM-480”” (a long chain epoxy type silane coupling agent), allavailable from Shin-Etsu Chemical Co., Ltd. The surface treatment agentsmay be used alone or in combination of two or more kinds thereof.

The degree of surface treatment with the surface treatment agent can beevaluated by the amount of carbon per unit surface area of the inorganicfiller. In order to enhance the dispersibility of the inorganic filler,the amount of carbon per unit surface area of the inorganic filler ispreferably 0.02 mg/m² or more, more preferably 0.1 mg/m² or more, andfurther preferably 0.2 mg/m² or more. In order to suppress an increasein the melt viscosity of resin varnish and the melt viscosity in a sheetform, the amount of carbon per unit surface area of the inorganic filleris preferably 1 mg/m² or less, more preferably 0.8 mg/m² or less, andfurther preferably 0.5 mg/m² or less.

The amount of carbon per unit surface area of the inorganic filler canbe measured after the surface-treated inorganic filler is washed with asolvent such as methyl ethyl ketone (MEK). Specifically, a sufficientamount of MEK is added as the solvent to the inorganic filler which issurface-treated with the surface treatment agent, and the resultantmixture is washed by ultrasonication at 25° C. for 5 minutes. Asupernatant liquid is removed and a solid content is dried. The amountof carbon per unit surface area of the inorganic filler can be measuredusing a carbon analyzer. As the carbon analyzer, “EMIA-320V”manufactured by Horiba Ltd., or the like can be used.

The content (filling amount) of the inorganic filler in the resincomposition is 50% by mass or more, preferably 55% by mass or more, andmore preferably 60% by mass or more when the nonvolatile component inthe resin composition layer is determined to be 100% by mass from theviewpoint of improving the thickness stability of the resin compositionlayer. The upper limit of the content of the inorganic filler in theresin composition is preferably 85% by mass or less and more preferably80% by mass or less from the viewpoint of improving the thin filminsulating property and the tensile breaking strength of the insulatinglayer (a cured product of the resin composition layer).

(D) Thermoplastic Resin

The resin composition of the present invention may further contain (D) athermoplastic resin.

Examples of the thermoplastic resin may include a phenoxy resin, apolyvinyl acetal resin, a polyolefine resin, a polybutadiene resin, apolyimide resin, a polyamideimide resin, a polyetherimide resin, apolysulfone resin, a polyether sulfone resin, a polyphenylene etherresin, a polycarbonate resin, a polyetherether ketone resin, and apolyester resin. A phenoxy resin is preferable. The thermoplastic resinmay be used alone or in combination of two or more kinds thereof.

The polystyrene-equivalent weight average molecular weight of thethermoplastic resin is preferably in a range of 8,000 to 70,000, morepreferably in a range of 10,000 to 60,000, and further preferably in arange of 20,000 to 60,000. The polystyrene-equivalent weight averagemolecular weight of the thermoplastic resin is measured by the gelpermeation chromatography (GPC) method. Specifically, thepolystyrene-equivalent weight average molecular weight of thethermoplastic resin can be determined by measurement using LC-9A/RID-6Amanufactured by Shimadzu Corporation as a measurement apparatus, ShodexK-800P/K-804L/K-804L manufactured by Showa Denko K.K., as columns, andchloroform or the like as a mobile phase. The measurement is performedat a column temperature of 40° C., and the polystyrene-equivalent weightaverage molecular weight can be computed using a standard polystyrenecalibration curve.

Examples of the phenoxy resin may include phenoxy resins having one ormore skeletons selected from the group consisting of a bisphenol Askeleton, a bisphenol F skeleton, a bisphenol S skeleton, a bisphenolacetophenone skeleton, a novolac skeleton, a biphenyl skeleton, afluorene skeleton, a dicyclopentadiene skeleton, a norbornene skeleton,a naphthalene skeleton, an anthracene skeleton, an adamantane skeleton,a terpene skeleton, and a trimethyl cyclohexane skeleton. A terminalends of the phenoxy resin may be any functional group such as a phenolichydroxyl group and an epoxy group. The phenoxy resin may be used aloneor in combination of two or more kinds thereof. Specific examples of thephenoxy resin may include “1256” and “4250” (both bisphenol Askeleton-containing phenoxy resins), “YX8100” (bisphenol Sskeleton-containing phenoxy resin), and “YX6954” (bisphenol acetophenoneskeleton-containing phenoxy resin) available from Mitsubishi ChemicalCorporation. Additional examples thereof may include “FX280” and “FX293”available from Nippon Steel & Sumikin Chemical Co., Ltd., and“YX6954BH30,” “YX7553,” “YX7553BH30,” “YL7769BH30,” “YL6794,” “YL7213,”“YL7290,” and “YL7482” available from Mitsubishi Chemical Corporation.

Examples of the polyvinyl acetal resin may include a polyvinyl formalresin and a polyvinyl butyral resin, and a polyvinyl butyral resin ispreferable. Specific examples of the polyvinyl acetal resin include“Denka Butyral 4000-2”, “Denka Butyral 5000-A”, “Denka Butyral 6000-C”,and “Denka Butyral 6000-EP” available from Denka Company Limited, andS-LEC BH series, BX series (for example, BX-5Z), KS series (for example,KS-1), BL series, and BM series available from Sekisui Chemical Co.,Ltd.

Specific examples of the polyimide resin may include “RIKACOAT SN20” and“RIKACOAT PN20” available from New Japan Chemical Co., Ltd. Specificexamples of the polyimide resin may include modified polyimides such asa linear polyimide obtained by reaction of a difunctionalhydroxyl-terminated polybutadiene, a diisocyanate compound, and atetrabasic acid anhydride (polyimide described in Japanese PatentApplication Laid-Open No. 2006-37083, which is incorporated herein byreference in its entirety), and a polysiloxane skeleton-containingpolyimide (polyimide described in Japanese Patent Application Laid-OpenNos. 2002-12667 and 2000-319386, which are incorporated herein byreference in their entireties).

Specific examples of the polyamideimide resin may include “VYLOMAXHR11NN” and “VYLOMAX HR16NN” available from Toyobo Co., Ltd. Additionalexamples of the polyamideimide resin may include modifiedpolyamideimides such as “KS9100” and “KS9300” (polysiloxaneskeleton-containing polyamideimide) available from Hitachi ChemicalCompany, Ltd.

Specific examples of the polyethersulfone resin may include “PES5003P”available from Sumitomo Chemical Co., Ltd.

Specific examples of the polysulfone resin may include polysulfones“P1700” and “P3500” available from Solvay Advanced Polymers K.K.

Among them, the phenoxy resin and the polyvinyl acetal resin arepreferable as the thermoplastic resin. Consequently, in a preferredembodiment, the thermoplastic resin contains one or more selected fromthe group consisting of the phenoxy resin and the polyvinyl acetalresin.

When the resin composition contains the thermoplastic resin, the contentof the thermoplastic resin is preferably 0.5% by mass to 10% by mass,more preferably 0.6% by mass to 5% by mass, and further preferably 0.7%by mass to 3% by mass.

(E) Curing Accelerator

The resin composition of the present invention may further contains (E)a curing accelerator.

Examples of the curing accelerator may include a phosphorus-based curingaccelerator, an amine-based curing accelerator, an imidazole-basedcuring accelerator, a guanidine-based curing accelerator, a metalliccuring accelerator, and an organic peroxide-based curing accelerator. Aphosphorus-based curing accelerator, an amine-based curing accelerator,an imidazole-based curing accelerator, and a metallic curing acceleratorare preferable, and an amine-based curing accelerator, animidazole-based curing accelerator, and a metallic curing acceleratorare more preferable. The curing accelerator may be used alone or incombination of two or more kinds thereof.

Examples of the phosphorus-based curing accelerator may includetriphenylphosphine, a phosphoniumborate compound, tetraphenylphosphoniumtetraphenylborate, n-butylphosphonium tetraphenylborate,tetrabutylphosphonium decanoate, (4-methylphenyl)triphenylphosphoniumthiocyanate, tetraphenylphosphonium thiocyanate, andbutyltriphenylphosphonium thiocyanate. Triphenylphosphine andtetrabutylphosphonium decanoate are preferable.

Examples of the amine-based curing accelerator may include trialkylaminesuch as triethylamine and tributylamine, 4-dimethylaminopyridine,benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and1,8-diazabicyclo[5,4.0]undecene. 4-Dimethylaminopyridine and1,8-diazabicyclo[5,4,0]-undecene are preferable.

Examples of the imidazole-based curing accelerator may include animidazole compound such as 2-methylimidazole, 2-undecylimidazole,2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole,1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole,2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole,1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole,1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole,1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazoliumtrimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate,2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-undecylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine, a2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine isocyanuricacid adduct, a 2-phenylimidazole isocyanuric acid adduct,2-phenyl-4,5-dihydroxymethylimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole,2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole,1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline,and 2-phenylimidazoline; and an adduct of such imidazole compound and anepoxy resin. 2-Ethyl-4-methylimidazole and 1-benzyl-2-phenylimidazoleare preferable.

As the imidazole-based curing accelerator, a commercially availableproduct may be used. Examples thereof may include “P200-H50” availablefrom Mitsubishi Chemical Corporation.

Examples of the guanidine-based curing accelerator may includedicyandiamide, 1-methylguanidine, 1-ethylguanidine,1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine,dimethylguanidine, diphenylguanidine, trimethylguanidine,tetramethylguanidine, pentamethylguanidine,1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1-methylbiguanide,1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide,1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide,1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide.Dicyandiamide and 1,5,7-triazabicyclo[4.4.0]dec-5-ene are preferable.

Examples of the metallic curing accelerator may include an organiccomplex and an organic salt of a metal such as cobalt, copper, zinc,iron, nickel, manganese, and tin. Specific examples of the organic metalcomplex may include an organic cobalt complex such as cobalt(II)acetylacetonate and cobalt(III) acetylacetonate, an organic coppercomplex such as copper(II) acetylacetonate, an organic zinc complex suchas zinc(II) acetylacetonate, an organic iron complex such as iron(III)acetylacetonate, an organic nickel complex such as nickel(II)acetylacetonate, and an organic manganese complex such as manganese(II)acetylacetonate. Examples of the organic metal salt may include zincoctylate, tin octylate, zinc naphthenate, cobalt naphthenate, tinstearate, and zinc stearate.

Examples of the organic peroxide-based curing accelerator may includedicumyl peroxide, cyclohexanone peroxide, tert-butyl peroxybenzoate,methyl ethyl ketone peroxide, dicumyl peroxide, tert-bythyl cumylperoxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide,cumene hydroperoxide, and tert-butyl hydroperoxide. As the organicperoxide-based curing accelerator, a commercially available product maybe used. Examples thereof may include “percumyl D” available from NOFcorporation.

The content of the curing accelerator in the resin composition is notparticularly limited and is preferably 0.01% by mass to 3% by mass whenthe nonvolatile components in the epoxy resin and the curing agent aredetermined to be 100% by mass.

(F) Flame Retardant

The resin composition of the present invention may further contain (F) aflame retardant. Examples of the flame retardant may include an organicphosphorus-based flame retardant, an organic nitrogen-containingphosphorus compound, a nitrogen compound, a silicone-based flameretardant, and metal hydroxide. The flame retardant may be used alone orin combination of two or more kinds thereof.

As the flame retardant, a commercially available product may be used.Examples thereof may include “HCA-HQ” available from Sanko Co., Ltd.,and “PX-200” available from Daihachi Chemical Industry Co., Ltd. As theflame retardant, flame retardants that are difficult to be hydrolyzedare preferable and, for example, 10-(2,5-dihydroxyphenyl)- and the likeare preferable.

When the resin composition includes the flame retardant, the content ofthe flame retardant is not particularly limited and is preferably 0.5%by mass to 20% by mass, more preferably 0.5% by mass to 15% by mass, andfurther preferably 0.5% by mass to 10% by mass.

(G) Organic Filler

The resin composition may contain (G) an organic filler from theviewpoint of improving a tensile breaking strength of a cured product ofthe resin composition layer. As the organic filler, any organic fillerthat may be used for forming an insulating layer of a printed wiringboard may be used. Examples thereof may include rubber particles,polyamide fine particles, and silicone particles.

As the rubber particles, commercially available products may be used.Examples thereof may include “EXL2655” available from Dow Chemical JapanLtd. and “AC3401N” and “AC3816N” available from Aica Kogyo Company,Limited.

For example, “AC3816N” and “AC3401N” available from Aica Kogyo Company,Limited are preferable as the rubber particles from the viewpoint ofproviding a low ionic property and allowing an extracted waterconductivity of a cured product of the resin composition layer to belowered.

When the resin composition includes the organic filler, the content ofthe organic filler is preferably 0.1% by mass to 20% by mass, morepreferably 0.2% by mass to 10% by mass, further preferably 0.3% by massto 5% by mass or 0.5% by mass to 3% by mass.

(H) Other Additives

The resin composition may further contain other additive, if necessary.Examples of the other additive may include an organometallic compoundsuch as an organic copper compound, an organic zinc compound, and anorganic cobalt compound, and a resin additive such as a thickener, anantifoaming agent, a leveling agent, an adhesion-imparting agent, and acoloring agent.

The resin sheet of the present invention provides an insulating layer (acured product of a resin composition layer) having excellent thin filminsulating properties. Therefore, the resin sheet of the presentinvention can be suitably used as a resin sheet in order to form aninsulating layer of a printed wiring board (for forming an insulatinglayer of a printed wiring board) and can be more suitably used as aresin sheet in order to form an interlayer insulating layer of a printedwiring board (a resin sheet for an interlayer insulating layer of aprinted wiring board). For example, in a printed wiring board includinga first conductive layer, a second conductive layer, and an insulatinglayer provided between the first conductive layer and the secondconductive layer, excellent insulating property can be achieved evenwhen a thickness of the insulating layer between the first and thesecond conductive layers is 6 μm or less (preferably 5.5 μm or less andmore preferably 5 μm or less) by forming the insulating layer using theresin sheet of the present invention. In a preferred embodiment, theresin sheet of the present invention is used for forming an insulatinglayer of a printed wiring board including a first conductive layer, asecond conductive layer, and the insulating layer that insulates thefirst conductive layer from the second conductive layer and has athickness of 6 μm or less between the first conductive layer and thesecond conductive layer.

Resin Sheet

The resin sheet of the present invention includes a support and a resincomposition layer provided on the support. The resin composition layeris formed from the resin composition.

The thickness of the resin composition layer is preferably 15 μm orless, more preferably 12 μm or less, further preferably 10 μm or less,and further more preferably 8 μm or less from the viewpoint of makingthe thickness of the printed wiring board thinner. The lower limit ofthe thickness of the resin composition layer is not particularly limitedand may be determined to be usually 1 μm or more, 1.5 μm or more, or 2μm or more.

Examples of the support may include a film of a plastic material, ametal foil, and a release paper. The film of a plastic material and themetal foil is preferable.

When the film of a plastic material is used as the support, examples ofthe plastic material may include polyester such as polyethyleneterephthalate (hereinafter may be abbreviated as “PET”) and polyethylenenaphthalate (hereinafter may be abbreviated as “PEN”), polycarbonate(hereinafter may be abbreviated as “PC”), acryl such as polymethylmethacrylate (PMMA), cyclic polyolefin, triacetyl cellulose (TAC),polyether sulfide (PES), polyether ketone, and polyimide. Among them,polyethylene terephthalate and polyethylene naphthalate are preferable,and inexpensive polyethylene terephthalate is particularly preferable.

When the metal foil is used as the support, examples of the metal foilmay include a copper foil and an aluminum foil. The copper foil ispreferable. As the copper foil, a foil made of a single metal of coppermay be used. Alternatively, a foil made of an alloy of copper andanother metal (for example, tin, chromium, silver, magnesium, nickel,zirconium, silicon, or titanium) may be used.

A surface of the support which is to be in contact with the resincomposition layer may be subjected to a mat treatment, a coronatreatment or an antistatic treatment.

As the support, a support with a release layer which has a release layeron a surface to be in contact with the resin composition layer may beused. Examples of a release agent used for the release layer of thesupport with a release layer may include one or more release agentsselected from the group consisting of an alkyd resin, a polyolefinresin, a urethane resin, and a silicone resin. As the support with arelease layer, a commercially available product may be used. Examplesthereof may include “SK-1,” “AL-5,” and “AL-7” available from LintecCorporation and “Lumirror T6AM” and “Lumirror R80” available from TorayIndustries, Inc., which are PET films with a release layer containing analkyd resin-based release agent as a main component.

The thickness of the support is not particularly limited, and ispreferably in a range of 5 μm to 75 μm and more preferably in a range of10 μm to 60 μm. When the support with a release layer is used, it ispreferable that the total thickness of the support with a release layerfalls within the above-described range.

The resin sheet can be produced, for example, by preparing a resinvarnish in which a resin composition is dissolved in an organic solvent,applying the resin varnish to the support using a die coater or thelike, and drying the resin varnish to form the resin composition layer.

Examples of the organic solvent may include ketones such as acetone,methyl ethyl ketone (MEK), and cyclohexanone, acetate esters such asethyl acetate, butyl acetate, cellosolve acetate, propylene glycolmonomethyl ether acetate, and carbitol acetate, carbitols such ascellosolve and butyl carbitol, aromatic hydrocarbons such as toluene andxylene, and amide-based solvents such as dimethylforamide,dimethylacetamide (DMAc), and N-methyl pyrrolidone. The organic solventmay be used alone or in combination of two or more kinds thereof.

The resin varnish may be dried by a publicly known method such asheating and blowing hot air. Although a drying condition is notparticularly limited, the resin varnish is dried so that the content ofthe organic solvent in the resin composition layer is 10% by mass orless, and preferably 5% by mass or less. When, for example, a resinvarnish containing 30% by mass to 60% by mass of organic solvent isused, the resin varnish is dried at 50° C. to 150° C. for 3 minutes to10 minutes, whereby a resin composition layer can be formed. However,these conditions vary depending on the boiling point of the solvent inthe resin varnish.

In the resin sheet, a protection film that is similar to the support canbe further laminated onto a surface of the resin composition layer thatis not in contact with the support (that is, a surface on a sideopposite to the support). The thickness of the protection film is notparticularly limited and is, for example, 1 μm to 40 μm. By laminatingthe protection film, adhesion of dust or the like or occurrence ofscratch on the surface of the resin composition layer can be prevented.The resin sheet can be wound into a roll form and stored. When the resinsheet has a protection film, the resin sheet can be used by peeling offthe protection film.

The lowest melt viscosity of the resin composition layer in the resinsheet is preferably 12,000 poise (1,200 Pa·s) or less, more preferably10,000 poise (1,000 Pa·s) or less, and further preferably 8,000 poise(800 Pa·s) or less, 5,000 poise (500 Pa·s) or less, or 4,000 poise (400Pa·s) or less from the viewpoint of obtaining an excellent circuitembeddability. The lower limit of the lowest melt viscosity ispreferably 1,000 poise (100 Pa·s) or more, more preferably 1,500 poise(150 Pa·s) or more, and further preferably 2,000 poise (200 Pa·s) ormore from the viewpoint of stably maintaining a thickness even when theresin composition layer is thin.

The lowest melt viscosity of the resin composition layer is the lowestviscosity of the resin composition layer when the resin of the resincomposition layer is melted. Specifically, when the resin compositionlayer is heated at a constant rate of temperature rise to melt theresin, the melt viscosity is decreased with increasing temperature at aninitial stage and then the melt viscosity is increased with increasingtemperature as the temperature becomes higher than a certain level. Thelowest melt viscosity is a melt viscosity at the time when the meltviscosity becomes a minimum. The lowest melt viscosity of the resincomposition layer can be measured by a dynamic viscoelasticity method,for example, in accordance with the method described in “Measurement oflowest melt viscosity” described below.

Cured Product

The cured product obtained by thermally curing the resin compositionlayer of the resin sheet of the present invention satisfies at least oneof a specific extracted water conductivity (Property 1) and a specificratio of a tensile breaking strength (Property 2). The present inventioncan provide an insulating layer having excellent thin layer insulatingproperty since a cured product of the resin composition layer of thepresent invention satisfies the following properties.

Property 1

An extracted water conductivity A of a cured product of the resincomposition layer when extracted at 120° C. for 20 hours is 50 μS/cm orless and an extracted water conductivity B of a cured product of theresin composition layer when extracted at 160° C. for 20 hours is 200μS/cm or less.

Property 2

A ratio (B/A) of a tensile breaking strength B of a 10 μm thicknesscured product of the resin composition layer after HAST test to atensile breaking strength A of a 10 μm thickness cured product of theresin composition layer is 0.65 or more and 1 or less.

The cured product of the resin composition layer satisfying Property 1can be obtained by using a resin having high purity, using a resindifficult to be hydrolyzed, or using a resin having high heat resistancefor the components contained in the resin composition (for example, theepoxy resin and the curing agent), or adjusting an amount of theinorganic filler.

The cured product of the resin composition layer satisfying Property 2can be obtained by using a resin having high purity, using a resindifficult to be hydrolyzed, or using a resin having high heat resistancefor the components contained in the resin composition (for example, theepoxy resin and the curing agent), or adjusting an amount of theinorganic filler.

In the present invention, an insulating layer having excellent thin filminsulating properties can be provided as long as a cured product of theresin composition layer satisfies any one of Property 1 and Property 2.The cured product of the resin composition layer having both of Property1 and Property 2, however, is preferable because it can provide aninsulating layer having more excellent thin film insulating properties.

The thermal curing condition of resin composition layer of the resinsheet of the present invention is not particularly limited. For example,the condition usually employed in formation of an insulating layer of aprinted wiring board described below may be used. The resin compositionmay be preheated before thermal curing. The heat treatment including thepreheating may be carried out several times in the thermal curingcondition. In an example of the thermal curing condition, the resincomposition is thermally cured firstly at 100° C. for 30 minutes, thenat 175° C. for 30 minutes, and further at 190° C. for 90 minutes.

From the viewpoint of providing an insulating layer having excellentthin film insulating property, an extracted water conductivity A of acured product (for example, a cured product obtained by thermally curingthe resin composition layer at 100° C. for 30 minutes, then at 175° C.for 30 minutes, and further at 190° C. for 90 minutes) of the resincomposition layer of the present resin sheet when extracted at 120° C.for 20 hours is 50 μS/cm or less and an extracted water conductivity Bof a cured product of the resin composition layer when extracted at 160°C. for 20 hours is 200 μS/cm or less. The extracted water conductivity Ais preferably 47 μS/cm or less, more preferably 45 μS/cm or less, andfurther preferably 43 μS/cm or less. The extracted water conductivity Bis preferably 195 μS/cm or less, more preferably 190 μS/cm or less, andfurther preferably 185 μS/cm or less from the viewpoint of achieving aninsulating layer having excellent thin film insulating property. Theextracted water conductivity A of a cured product of the resincomposition layer when extracted at 120° C. for 20 hours and theextracted water conductivity B of a cured product of the resincomposition layer when extracted at 160° C. for 20 hours can be measuredin accordance with the method described in “Measurement of extractedwater conductivity of cured product” mentioned below.

A glass transition temperature (measured by DMA) of a cured product (forexample, a cured product obtained by thermally curing the resincomposition layer at 100° C. for 30 minutes, then at 175° C. for 30minutes, and further at 190° C. for 90 minutes) of the resin compositionlayer of the present resin sheet is preferably 160° C. or more, morepreferably 170° C. or more, and further preferably 180° C. or more fromthe viewpoint of allowing the extracted water conductivity of a curedproduct of the resin composition layer to be easily lowered andsuppressing deterioration in the tensile breaking strength when thecured product of the resin composition layer is placed under ahigh-temperature and high-humidity environment. The glass transitiontemperature of a cured product of the resin composition layer can bemeasured, for example, in accordance with the method described in“Measurement of glass transition temperature of cured product”.

A tensile breaking strength A of a 10 μm thickness cured product (forexample, a cured product obtained by thermally curing the resincomposition layer at 100° C. for 30 minutes, then at 175° C. for 30minutes and, further at 190° C. for 90 minutes) of the resin compositionlayer of the present resin sheet is preferably 50 MPa or more, morepreferably 60 MPa or more, and further preferably 70 MPa or more fromthe viewpoint of achieving an insulating layer having an excellent thinfilm insulating property. The upper limit of the tensile breakingstrength A is not particularly limited and may be, for example, 150 MPaor less, 140 MPa or less, 130 MPa or less, 120 MPa or less, or 110 MPaor less.

A tensile breaking strength B after a HAST test of a 10 μm thicknesscured product (for example, a cured product obtained by thermally curingthe resin composition layer at 100° C. for 30 minutes, then at 175° C.for 30 minutes, and further at 190° C. for 90 minutes) of the resincomposition layer of the present resin sheet is preferably 50 MPa ormore, more preferably 55 MPa or more, further preferably 60 MPa or more,and further more preferably 70 MPa or more from the viewpoint ofachieving an insulating layer having excellent thin film insulatingproperties. The upper limit of the tensile breaking strength B is notparticularly limited and may be, for example, 150 MPa or less, 140 MPaor less, 130 MPa or less, 120 MPa or less, or 110 MPa or less. In thepresent invention, the HAST (Highly Accelerated temperature and humidityStress Test) test can be carried out, for example, by using a highlyaccelerated life test apparatus (“PM422” manufactured by ETACEngineering Co., Ltd.) and subjecting a cured product of the resincomposition layer to the condition of a relative humidity of 85% at 130°C. for 100 hours.

In the present invention, the ratio (B/A) of the tensile breakingstrength B to the tensile breaking strength A is preferably 0.65 ormore, more preferably 0.68 or more, and further preferably 0.70 or morefrom the viewpoint of achieving an insulating layer having excellentthin film insulating property. The ratio (B/A) of the tensile breakingstrength B to the tensile breaking strength A is preferably 1 or less,more preferably 0.9 or less, and further preferably 0.8 or less from theviewpoint of achieving an insulating layer having excellent thin filminsulating property.

For cured products of the resin composition layer of the present resinsheet, the tensile breaking strength A of a 10 μm thickness curedproduct and the tensile breaking strength B after a HAST test of a 10 μmthickness cured product can be measured, for example, in accordance withthe method described in “Measurement of tensile breaking strength ofcured product” noted below. The ratio (B/A) of the tensile breakingstrength B to the tensile breaking strength A can be calculated usingthe measured values obtained by the measurement.

The cured product obtained by thermally curing the resin compositionlayer of the present resin sheet (for example, a cured product obtainedby thermally curing the resin composition at 100° C. for 30 minutes andthen at 175° C. for 30 minutes) exhibits an excellent insulationresistance value even after subjected to the environment of 130° C., 85RH %, and 3.3 V application for 100 hours. In other words, the curedproduct provides an insulating layer exhibiting excellent insulationresistance value. The upper limit of the insulation resistance value ispreferably 10¹²Ω or less, more preferably 10¹¹Ω or less, and furtherpreferably 10¹⁰Ω or less. The lower limit is not particularly limitedand is preferably 10⁶Ω or more and more preferably 10⁷Ω or more. Theinsulation resistance value can be measured in accordance with themethod described in “Evaluation of insulation reliability andmeasurement of thickness of insulating layer between conductive layer”noted below.

The present invention also includes a cured product of the resincomposition layer in which the extracted water conductivity A whenextracted at 120° C. for 20 hours is 50 μS/cm or less and the extractedwater conductivity B when extracted at 160° C. for 20 hours is 200 μS/cmor less. The cured product has the same configuration as the curedproduct of the resin composition layer of the resin sheet of the presentinvention. The curing condition of the resin composition for forming thecured product is the same as the curing condition of the resin sheet. Inthe cured product of the present invention (for example, a cured productobtained by thermally curing the resin composition layer at 100° C. for30 minutes, then at 175° C. for 30 minutes, and further at 190° C. for90 minutes), the preferable range of the extracted water conductivity Aand the preferable range of the extracted water conductivity B are thesame as those of the cured product of the resin sheet described above.The preferable ranges of the other physical properties than theextracted water conductivity of the cured product (a glass transitiontemperature, a tensile breaking strength A, a tensile breaking strengthB, a ratio of the tensile breaking strength B to the tensile breakingstrength A (B/A), and an insulation resistance value) are also the sameas those of the cured products of the resin sheet described above.

Printed Wiring Board and Method for Producing the Same

The printed wiring board of the present invention includes an insulatinglayer formed of a cured product of the resin composition layer of thepresent resin sheet, a first conductive layer, and a second conductivelayer. The printed wiring board of the present invention may include thecured product of the present invention as the insulating layer. Theinsulating layer is provided between the first conductive layer and thesecond conductive layer and insulates the first conductive layer fromthe second conductive layer (the conductive layers are also referred toas wiring layers). The insulating layer formed of the cured product ofthe resin composition layer of the present resin sheet has excellentthin film insulating property, and thus exhibits excellent insulatingproperty even when a thickness of the insulating layer between the firstand second conductive layers is 6 μm or less.

The thickness of the insulating layer between the first and secondconductive layers is preferably 6 μm or less, more preferably 5.5 μm orless, and further preferably 5 μm or less. The lower limit thereof isnot particularly limited and may be 0.1 μm or more. As exemplarilyillustrated in FIG. 1, the thickness of the insulating layer between thefirst and second conductive layers means a thickness t1 of an insulatinglayer 7 between a main surface 51 of a first conductive layer 5 and amain surface 61 of a second conductive layer 6. The first and secondconductive layers are adjacent conductive layers with the insulatinglayer interposed there-between and the main surface 51 and the mainsurface 61 are opposed to each other. The thickness of the insulatinglayer between the first and second conductive layers can be measured inaccordance with the method described in “Evaluation of insulationreliability and measurement of thickness of insulating layer betweenconductive layers” noted below.

The thickness t2 of the entire insulating layer is preferably 20 μm orless, more preferably 15 μm or less, and further preferably 12 μm orless. The lower limit thereof is not particularly limited and may be 1μm or more.

The printed wiring board of the present invention can be produced by amethod including the following steps (I) and (II) using the resin sheetdescribed above:

(I) laminating the resin sheet on an internal layer substrate so thatthe resin composition layer of the resin sheet is in contact with theinternal layer substrate; and

(II) thermally curing the resin composition layer to form an insulatinglayer

The “internal layer substrate” used in the step (I) refers mainly to: asubstrate such as a glass epoxy substrate, a metal substrate, apolyester substrate, a polyimide substrate, a BT resin substrate and athermosetting polyphenylene ether substrate; and a circuit substrate inwhich a patterned conductive layer (circuit) is formed on one side orboth sides of the above substrate. The “internal layer substrate” in thepresent invention also includes an internal layer circuit substrate thatis an intermediate product on which an insulating layer and/or aconductive layer is further to be faulted in the production of a printedwiring board. In a case where the printed wiring board is adevice-embedded circuit board, an internal layer substrate including adevice embedded therein may be used.

The lamination of the resin sheet and the internal layer substrate canbe carried out by, for example, thermal pressing the resin sheet to theinternal layer substrate from the support side. Examples of a memberused for thermal pressing the resin sheet to the internal layersubstrate (hereinafter referred to as a “thermal pressing member”) mayinclude a heated metal plate such as a stainless (SUS) flat panel and aheated metal roll (SUS roll). The thermal pressing member is preferablypressed against the resin sheet in a state that an elastic material suchas heat resistant rubber intervenes there-between so as to allowing theresin sheet to sufficiently follow the surface irregularities of theinternal layer substrate, instead of directly pressing the thermalpressing member against the resin sheet.

The lamination of the internal layer substrate and the resin sheet maybe carried out by a vacuum lamination method. In the vacuum laminationmethod, the thermal pressing temperature is preferably in a range of 60°C. to 160° C. and more preferably in a range of 80° C. to 140° C., thethermal pressing pressure is preferably in a range of 0.098 MPa to 1.77MPa and more preferably in a range of 0.29 MPa to 1.47 MPa, and thethermal pressing time is preferably in a range of 20 seconds to 400seconds and more preferably in a range of 30 seconds to 300 seconds. Itis preferable that the lamination is carried out under a reducedpressure condition of 26.7 hPa or less.

The lamination can be carried out by a commercially available vacuumlaminator. Examples of the commercially available vacuum laminator mayinclude a vacuum pressure laminator manufactured by MEIKI CO., LTD. anda vacuum applicator manufactured by Nikko Materials Co., Ltd.

After the lamination, the laminated resin sheet may be subjected to asmoothing treatment, for example, by pressing the thermally pressingmember from the support side under normal pressure (atmosphericpressure). A pressing condition for the smoothing treatment may be thesame as the thermal pressing condition for the lamination describedabove. In the smoothing treatment, a commercially available vacuumlaminator may be used. The laminating and the smoothing treatment may beperformed continuously using the commercially available vacuumlaminator.

The support may be removed between the step (I) and the step (II) or maybe removed after the step (II).

In the step (II), the resin composition layer is thermally cured to forman insulating layer.

The condition for thermal curing of the resin composition layer is notparticularly limited. The condition may be a condition that is usuallyemployed in formation of an insulating layer of a printed wiring board.

A condition for thermally curing the resin composition layer variesdepending on the type of the resin composition and the like. Forexample, the curing temperature is in a range of 120° C. to 240° C.(preferably in a range of 150° C. to 220° C. and more preferably in arange of 170° C. to 200° C.) and the curing time is in a range of 5minutes to 120 minutes (preferably 10 minutes to 100 minutes and morepreferably 15 minutes to 90 minutes).

Before thermally curing the resin composition layer, the resincomposition layer may be preheated at a temperature lower than thecuring temperature. For example, before thermally curing the resincomposition layer, the resin composition layer may be preheated at atemperature of 50° C. or more and less than 120° C. (preferably 60° C.or more and 110° C. or less and more preferably 70° C. or more and 100°C. or less) for 5 minutes or more (preferably 5 minutes to 150 minutesand more preferably 15 minutes to 120 minutes).

When a printed wiring board is produced, a step (III) of perforating theinsulating layer, a step (IV) of roughening the insulating layer, and astep (V) of forming the conductive layer may be further performed. Thesesteps (III) to (V) may be performed by any methods that are known tothose skilled in the art in the production of a printed wiring board.When the support is removed after the step (II), removal of the supportmay be carried out between the step (II) and the step (III), between thestep (III) and the step (IV), or between the step (IV) and the step (V).The formation of the insulating layer and the conductive layer of thesteps (II) to (V) may be repeated to form a multilayer wiring board, ifnecessary. In this case, it is preferable that the thickness (t1 inFIG. 1) of each insulating layer between the conductive layers fallswithin the above range.

The step (III) is a step of perforating the insulating layer, wherebyholes such as via holes and through holes can be formed in theinsulating layer. The step (III) may be performed using, for example, adrill, laser, or plasma depending on the composition of the resincomposition used for forming the insulating layer or the like. The sizeand shape of the hole may be appropriately determined in accordance withthe design of the printed wiring board.

The step (IV) is a step of roughening the insulating layer. Theprocedure and condition for roughening are not particularly limited, andpublicly known procedure and condition that are generally used information of an insulating layer of a printed wiring board may be used.In the step (IV), the insulating layer may be roughened by a swellingtreatment with a swelling solution, a roughening treatment with anoxidant, and a neutralization treatment with a neutralization solutionin this order. The swelling solution is not particularly limited, andexamples thereof may include an alkaline solution and a surfactantsolution. An alkaline solution is preferable. As the alkaline solution,a sodium hydroxide solution and a potassium hydroxide solution arepreferable. Examples of a commercially available swelling solution mayinclude “Swelling Dip Securiganth P” and “Swelling Dip Securiganth SBU”available from Atotech Japan K. K. The swelling treatment with theswelling solution is not particularly limited, and for example, can beperformed by immersing the insulating layer into the swelling solutionat 30° C. to 90° C. for 1 minute to 20 minutes. From the viewpoint ofcontrolling the swelling of resin in the insulating layer to anappropriate level, it is preferable to immerse the insulating layer intothe swelling liquid at 40° C. to 80° C. for 5 minutes to 15 minutes. Theoxidant is not particularly limited, and examples thereof may include analkaline permanganate solution in which potassium permanganate or sodiumpermanganate is dissolved in an aqueous solution of sodium hydroxide.The roughening treatment with the oxidant such as the alkalinepermanganate solution is preferably performed by immersing theinsulating layer into an oxidant solution that is heated at 60° C. to80° C. for 10 minutes to 30 minutes. The concentration of permanganatein the alkaline permanganate solution is preferably 5% by mass to 10% bymass. Examples of a commercially available oxidant may include analkaline permanganate solution such as “Concentrate Compact CP” and“Dosing Solution Securiganth P” available from Atotech Japan K.K. It ispreferable that the neutralization solution be an acidic aqueoussolution. Examples of a commercially available product may include“Reduction Solution Securiganth P” available from Atotech Japan K.K. Thetreatment with the neutralization solution may be performed by immersingthe insulating layer a surface of which has been roughened with theoxidant solution into the neutralization solution at 30° C. to 80° C.for 5 minutes to 30 minutes. From the viewpoint of workability and thelike, a method of immersing the object that has been subjected to theroughening treatment with the oxidizing agent into the neutralizingliquid at 40° C. to 70° C. for 5 minutes to 20 minutes is preferable.

In one embodiment, the arithmetic mean roughness Ra of a surface of theinsulating layer after the roughening treatment is preferably 400 nm orless, more preferably 350 nm or less, further preferably 300 nm or less,250 nm or less, 200 nm or less, 150 nm or less, or 100 nm or less. Thearithmetic mean roughness (Ra) of a surface of the insulating layer canbe measured using a non-contact type surface roughness meter. Specificexamples of the non-contact type surface roughness meter may include“WYKO NT3300” manufactured by Veeco Instruments Inc.

The step (V) is a step of forming a conductive layer. When a conductivelayer is not formed on the internal layer substrate, the step (V) is astep of forming the first conductive layer. On the other hand, when aconductive layer is formed on the internal layer substrate, theconductive layer is the first conductive layer and the step (V) is astep of forming a second conductive layer.

A conductive material used for the conductive layer is not particularlylimited. In a preferred embodiment, the conductive layer includes one ormore metals selected from the group consisting of gold, platinum,palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel,titanium, tungsten, iron, tin, and indium. The conductive layer may be asingle metal layer or an alloy layer. Examples of the alloy layer mayinclude layers formed of an alloy of two or more metals selected fromthe above-described group such as a nickel-chromium alloy, acopper-nickel alloy, and a copper-titanium alloy. In particular, fromthe viewpoints of versatility of formation of the conductive layer,cost, and ease of patterning, the conductive layer is preferably asingle metal layer of chromium, nickel, titanium, aluminum, zinc, gold,palladium, silver or copper, or an alloy layer of a nickel-chromiumalloy, a copper-nickel alloy or a copper-titanium alloy; more preferablya single metal layer of chromium, nickel, titanium, aluminum, zinc,gold, palladium, silver or copper, or an alloy layer of anickel-chromium alloy; and further preferably a single metal layer ofcopper.

The conductive layer may have a single-layer structure or a multi-layerstructure in which two or more layers of single metal layer or alloylayer formed of different kinds of metals or alloys are layered. Whenthe conductive layer has a multi-layer structure, it is preferable thata layer in contact with the insulating layer be a single metal layer ofchromium, zinc or titanium or an alloy layer of nickel-chromium alloy.

The thickness of the conductive layer varies depending on a desireddesign of a printed wiring board, and is generally 3 μm to 35 μm, andpreferably 5 μm to 30 μm.

In one embodiment, the conductive layer may be formed by plating. Forexample, a conductive layer having a desired wiring pattern can beformed by plating the surface of the insulating layer through aconventionally known technique such as a semi-additive method and afull-additive method. Hereinafter, an example of forming the conductivelayer by the semi-additive method will be described.

Firstly, a plating seed layer is formed on the surface of the insulatinglayer by electroless plating. Subsequently, onto the formed plating seedlayer, a mask pattern is formed that exposes a portion of the platingseed layer corresponding to a desired wiring pattern. A metal layer isformed on the exposed plating seed layer by electrolytic plating, andthen the mask pattern is removed. After that, an unnecessary platingseed layer can be removed by etching or the like to form a conductivelayer having a desired wiring pattern.

The resin sheet of the present invention provides an insulating layerexcellent in device embeddability and thus can be suitably used evenwhen a printed wiring board is a device-embedded circuit board. Thedevice-embedded circuit board can be produced by a known productionmethod.

In one embodiment, the printed wiring board produced using the resinsheet of the present invention may include an insulating layer that is acured product of the resin composition layer of the present resin sheetand an embedded type wiring layer embedded in the insulating layer.

The printed wiring board produced by using the resin sheet of thepresent invention is characterized in that it can exhibit excellentinsulation reliability even when the thickness of the insulating layerbetween the first and second conductive layers is 6 μm or less. Theupper limit of the insulation resistance value after 100 hours under thecondition of 130° C., 85 RH %, and 3.3 V application is preferably 10¹²Ωor less, more preferably 10¹¹Ω or less, and further preferably 10¹⁰Ω orless. The lower limit thereof is not particularly limited and ispreferably 10⁶Ω or more, and more preferably 10⁷Ω or more. Theinsulation resistance value can be measured in accordance with themethod described in “Evaluation of insulation reliability andmeasurement of thickness of insulating layer between conductive layers”noted below.

Semiconductor Device

The semiconductor device of the present invention includes the printedwiring board of the present invention. The semiconductor device of thepresent invention can be produced using the printed wiring board of thepresent invention.

Examples of the semiconductor device may include various semiconductordevices used in electrical products such as a computer, a cellularphone, a digital camera and a television, and vehicles such as amotorcycle, an automobile, a train, a ship and an airplane.

The semiconductor device of the present invention can be produced bymounting a part (semiconductor chip) on a conducting part of the printedwiring board. The “conducting part” is a “part for conducting anelectric signal in the printed wiring board,” which may be positioned ona surface or an embedded part. The semiconductor chip is notparticularly limited as long as it is an electric circuit element madeof a semiconductor as a material.

A method for mounting the semiconductor chip in production of thesemiconductor device of the present invention is not particularlylimited as long as the semiconductor chip effectively functions.Specific examples of the method may include a wire bonding mountingmethod, a flip-chip mounting method, a mounting method using a bumplessbuild-up layer (BBUL), a mounting method using an anisotropic conductivefilm (ACF), and a mounting method using a non-conductive film (NCF). The“method of mounting by bumpless build-up layer (BBUL)” is “a mountingmethod in which a semiconductor chip is embedded directly in a concaveportion of a printed wiring board, followed by connecting thesemiconductor chip to the wiring on the printed wiring board.”

Other features of the invention will become apparent in the course ofthe following descriptions of exemplary embodiments which are given forillustration of the invention and are not intended to be limitingthereof.

EXAMPLES

In the following description, “part” and “%” represent “part by mass”and “% by mass”, respectively, unless otherwise specified.

Measuring Method of Physical Properties of Inorganic Filler First, therewill be described the method of measuring the physical properties of theinorganic filler used in Examples and Comparative Examples.

Measurement of Average Particle Diameter

100 mg of an inorganic filler, 0.1 g of a dispersing agent (“SN9228”available from SAN NOPCO LIMITED), and 10 g of methyl ethyl ketone wereweighed in a vial bottle and dispersed by ultrasonication for 20minutes. The average particle diameter based on a median diameter wascalculated by measuring the particle size distribution in a batch cellmethod using a laser diffraction type particle size distributionmeasuring device (“SALD-2200” manufactured by Shimadzu Corporation).

Measurement of Specific Surface Area

The specific surface area of the inorganic filler was measured using aBET full automatic specific surface area measuring apparatus (“MacsorbHM-1210” manufactured by Mountech Co., Ltd.).

Measurement of True Density

The true density of the inorganic filler was measured using MicroUltra-Pycnometer (“MUPY-21T”, manufactured by Quantachrome InstrumentsJapan G. K.).

Measurement of Carbon Amount

The amount of carbon per unit surface area of the inorganic filler wasmeasured in accordance with the following procedure. A sufficient amountof MEK as a solvent was added to the inorganic filler prepared inPreparation Examples and washed with ultrasonication at 25° C. for 5minutes. Subsequently, the supernatant was removed and the solid contentwas dried. The amount of carbon of the obtained solid was measured usinga carbon analyzer (“EMIA-320”” manufactured by HORIBA, Ltd.). The amountof carbon per unit surface area of the inorganic filler was calculatedbased on the measured amount of carbon and the mass and specific surfacearea of inorganic filler used.

Preparation of Resin Sheet

A resin composition (also referred to as “resin varnish”) used forproducing a resin sheet was prepared in accordance with the followingprocedure to prepare a resin sheet of Examples and Comparative Examples.

Preparation of Resin Composition 1

4 Parts of a bisphenol A type epoxy resin (“YD-8125G”, available fromNIPPON STEEL & SUMIKIN CHEMICAL CO., LTD., epoxy equivalent weight:about 174), 6 parts of a bixylenol type epoxy resin (“YX4000HK”,available from Mitsubishi Chemical Corporation, epoxy equivalent weight:about 185), 6 parts of a bisphenol AF type epoxy resin (“YL7760”,available from Mitsubishi Chemical Corporation, epoxy equivalent weight:about 238), 18 parts of a biphenyl type epoxy resin (“NC3000L” availablefrom Nippon Kayaku Co., Ltd., epoxy equivalent weight: about 272), 10parts of a phenoxy resin (“YX7553BH30”, available from MitsubishiChemical Corporation, a 1:1 solution of cyclohexanone:methyl ethylketone (MEK) having a solid content of 30% by mass) were heated anddissolved in a mixed solvent of 10 parts of solvent naphtha and 10 partsof cyclohexanone with stirring. After the resultant soliton was cooledto room temperature, 10 parts of a triazine skeleton-containing phenolnovolac-based curing agent (“LA7052” available from DIC Corporation,hydroxyl equivalent weight: about 120, MEK solution having a solidcontent of 60%), 12 parts of naphthol-based curing agent (“SN-495V”,available from NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD., hydroxyl groupequivalent weight: 231, a MEK solution having a solid content of 60%),10 parts of a carbodiimide resin (“V-03”, available from NisshinboChemical Inc., carbodiimide equivalent weight: 216, a toluene solutionhaving a nonvolatile component of 50% by mass), 1 part of an amine-basedcuring accelerator (4-dimethylaminopyridine (DMAP), a MEK solutionhaving a solid content of 5% by mass), swollen rubber particles made byswelling 2 parts of rubber particles (AC-3401N, available from AicaKogyo Company, Limited) in 10 parts of solvent naphtha at roomtemperature for 12 hours, and 110 parts of spherical silica(“SPH516-05”, available from NIPPON STEEL & SUMIKIN MATERIALS CO., LTD.,average particle diameter: 0.29 μm, specific surface area: 16.3 m²/g,true density: 2.25 g/cm³, product of specific surface area and truedensity: 36.7 (m²/g·g/cm³), carbon amount per unit surface area: 0.43mg/m²) surface-treated with an aminosilane-based coupling agent(“KBM573” available from Shin-Etsu Chemical Co., Ltd.) were mixedthereinto. The resultant mixture was homogeneously dispersed with ahigh-speed rotation mixer and thereafter filtrated with a cartridgefilter (“SHP020” available from ROKI TECHNO CO., LTD.), thus preparing aresin composition 1.

Preparation of Resin Composition 2

4 Parts of a naphthalene type epoxy resin (“HP4032SS”, available fromDIC Corporation, epoxy equivalent weight: about 144), 8 parts of anaphthylene ether type epoxy resin (“EXA-7311-G””, available from DICCorporation, epoxy equivalent weight: about 213), 15 parts of anaphthalene type epoxy resin (“ESN475V”, available from NIPPON STEEL &SUMIKIN CHEMICAL CO., LTD., epoxy equivalent weight: about 330), and 6parts of a phenoxy resin (“YX7553BH30”, available from MitsubishiChemical Corporation, a 1:1 solution of cyclohexanone:methyl ethylketone (MEK) having a solid content of 30% by mass) were heated anddissolved in a mixed solvent of 15 parts of solvent naphtha and 10 partsof cyclohexanone with stirring. After the resultant soliton was cooledto room temperature, 18 parts of a prepolymer of bisphenol A dicyanate(“BA230S75”, available from Lonza Japan Co., Ltd., cyanate equivalentweight: about 232, a MEK solution having a nonvolatile content of 75% bymass), 10 parts of a multifunctional cyanate ester resin (“ULL-950S”,available from Lonza Japan Co., Ltd., cyanate equivalent weight: about230, a MEK solution having a nonvolatile content of 75% by mass), 6parts of an active ester-based curing agent (“HPC-8000-65T”, availablefrom DIC Corporation, an active group equivalent weight: about 225, atoluene solution having a nonvolatile component of 65%), 0.4 part of anamine-based curing accelerator (4-dimethylaminopyridine (DMAP), a MEKsolution having a solid content of 5% by mass), 3 parts of a curingaccelerator (cobalt (III) acetylacetonate (Co (III) Ac), available fromTokyo Chemical Industry Co., Ltd., a MEK solution having a solid contentof 1% by mass), and 90 parts of spherical silica (“SPH516-05”, availablefrom NIPPON STEEL & SUMIKIN MATERIALS CO., LTD., average particlediameter: 0.29 μm, specific surface area: 16.3 m²/g, true density: 2.25g/cm³, product of specific surface area and true density: 36.7(m²/g·g/cm³), carbon amount per unit surface area: 0.43 mg/m²)surface-treated with an aminosilane-based coupling agent (“KBM573”available from Shin-Etsu Chemical Co., Ltd.) were mixed thereinto. Theresultant mixture was homogeneously dispersed with a high-speed rotationmixer and thereafter filtrated with a cartridge filter (“SHP020”available from ROKI TECHNO CO., LTD.), thus preparing a resincomposition 2.

Preparation of Resin Composition 3

4 Parts of a glycidylamine type epoxy resin (“630LSD”, available fromMitsubishi Chemical Corporation, epoxy equivalent weight: about 95), 5parts of a bixylenol type epoxy resin (“YX4000HK”, available fromMitsubishi Chemical Corporation, epoxy equivalent weight: about 185), 5parts of a naphthylene ether type epoxy resin (“EXA-7311-G4”, availablefrom DIC Corporation, epoxy equivalent weight: about 213), 15 parts of abiphenyl type epoxy resin (“NC3000L” available from Nippon Kayaku Co.,Ltd., epoxy equivalent weight: about 272), and 10 parts of a phenoxyresin (“YX7553BH30”, available from Mitsubishi Chemical Corporation, a1:1 solution of cyclohexanone:methyl ethyl ketone (MEK) having a solidcontent of 30% by mass) were heated and dissolved in a mixed solvent of15 parts of solvent naphtha and 10 parts of cyclohexanone with stirring.After the resultant soliton was cooled to room temperature, 5 parts of atriazine skeleton-containing cresol novolac-based curing agent(“LA3018-50P”, available from DIC Corporation, hydroxyl equivalentweight: about 151, a 2-methoxypropanol solution having a solid contentof 50%), 15 parts of an active ester-based curing agent (“HPC-8000-65T”,available from DIC Corporation, active group equivalent weight: about225, a toluene solution having a nonvolatile component of 65% by mass),1.5 parts of an amine-based curing accelerator (4-dimethylaminopyridine(DMAP), a MEK solution having a solid content of 5% by mass), 2 parts ofa flame retardant (“HCA-HQ”, available from SANKO CO., LTD.,10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide,average particle size: 1.2 μm), and 110 parts of spherical silica(“SPH516-05”, available from NIPPON STEEL & SUMIKIN MATERIALS CO., LTD.,average particle diameter: 0.29 μm, specific surface area: 16.3 m²/g,true density: 2.25 g/cm³, product of specific surface area and truedensity: 36.7 (m²/g·g/cm³), carbon amount per unit surface area: 0.43mg/m²) surface-treated with an aminosilane-based coupling agent(“KBM573” available from Shin-Etsu Chemical Co., Ltd.) were mixedthereinto. The resultant mixture was homogeneously dispersed with ahigh-speed rotation mixer and thereafter filtrated with a cartridgefilter (“SHP020” available from ROKI TECHNO CO., LTD.), thus preparing aresin composition 3.

Preparation of Resin Composition 4

8 Parts of a bisphenol A type epoxy resin (“828EL”, available fromMitsubishi Chemical Corporation, epoxy equivalent weight: about 186), 6parts of a bisphenol AF type epoxy resin (“YL7760”, available fromMitsubishi Chemical Corporation, epoxy equivalent weight: about 238), 18parts of a biphenyl type epoxy resin (“NC3000L” available from NipponKayaku Co., Ltd., epoxy equivalent weight: about 272), 10 parts of aphenoxy resin (“YX7553BH30”, available from Mitsubishi ChemicalCorporation, a 1:1 solution of cyclohexanone:methyl ethyl ketone (MEK)having a solid content of 30% by mass) were heated and dissolved in amixed solvent of 5 parts of solvent naphtha and 10 parts ofcyclohexanone with stirring. After the resultant soliton was cooled toroom temperature, 10 parts of a triazine skeleton-containing phenolnovolac-based curing agent (“LA7052”, available from DIC Corporation,hydroxyl equivalent weight: about 120, a MEK solution having a solidcontent of 60%), 12 parts of a naphthol-based curing agent (“SN-495V””,available from NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD., hydroxyl groupequivalent weight: 231, a MEK solution having a solid content of 60%), 5parts of a block type isocyanate resin (“BURNOCK D-500”, available fromDIC Corporation, an ethyl acetate solution having a nonvolatilecomponent of 65% by mass), 1 part of an amine-based curing accelerator(4-dimethylaminopyridine (DMAP), a MEK solution having a solid contentof 5% by mass), swollen rubber particles made by swelling 6 parts ofrubber particles (AC-3355, available from Aica Kogyo Company, Limited)in 15 parts of solvent naphtha at room temperature for 12 hours, and 110parts of spherical silica (“ADMAFINE SO-C1”, available from AdmatechsCompany Limited, average particle diameter 0.63 μm, specific surfacearea 11.2 m²/g, true density 2.25 g/cm³, product of specific surfacearea and true density 25.2 (m²/g·g/cm³), amount of carbon per unitsurface area 0.35 mg/m²) treated its surface with an aminosilane-basedcoupling agent (“KBM573” available from Shin-Etsu Chemical Co., Ltd.)were mixed thereinto. The resultant mixture was homogeneously dispersedwith a high-speed rotation mixer and thereafter filtrated with acartridge filter (“SHP030” available from ROKI TECHNO CO., LTD.), thuspreparing a resin composition 4.

Preparation of Resin Composition 5

4 Parts of a naphthalene type epoxy resin (“HP4032SS”, available fromDIC Corporation, epoxy equivalent weight: about 144), 8 parts of abisphenol A type epoxy resin (“828EL”, available from MitsubishiChemical Corporation, epoxy equivalent weight: about 186), 15 parts of anaphthalene type epoxy resin (“ESN475V”, available from NIPPON STEEL &SUMIKIN CHEMICAL CO., LTD., epoxy equivalent weight: about 330), and 6parts of a phenoxy resin (“YX7553BH30”, available from MitsubishiChemical Corporation, a 1:1 solution of cyclohexanone:methylethyl ketone(MEK) having a solid content of 30% by mass) were heated and dissolvedin a mixed solvent of 10 parts of solvent naphtha and 10 parts ofcyclohexanone with stirring. After the resultant soliton was cooled toroom temperature, 18 parts of a prepolymer of bisphenol A dicyanate(“BA230S75”, available from Lonza Japan Co., Ltd., cyanate equivalentweight: about 232, a MEK solution having a nonvolatile content of 75% bymass), 10 parts of a multifunctional cyanate ester resin (“ULL-9505”,available from Lonza Japan Co., Ltd., cyanate equivalent weight: about230, a MEK solution having a nonvolatile content of 75% by mass), 6parts of a block type isocyanate resin (“BURNOCK D-500”, available fromDIC Corporation, an ethyl acetate solution having a nonvolatilecomponent of 65% by mass), 0.4 part of an amine-based curing accelerator(4-dimethylaminopyridine (DMAP), a MEK solution having a solid contentof 5% by mass), 3 parts of a curing accelerator (cobalt (III)acetylacetonate (Co(III) Ac), available from Tokyo Chemical IndustryCo., Ltd., a MEK solution having a solid content of 1% by mass), 90parts of spherical silica (“ADMAFINE SO-C1”, available from AdmatechsCompany Limited, average particle diameter 0.63 μm, specific surfacearea 11.2 m²/g, true density 2.25 g/cm³, product of specific surfacearea and true density 25.2 (m²/g·g/cm³), amount of carbon per unitsurface area 0.25 mg/m²) surface-treated with an epoxysilane-basedcoupling agent (“KBM403” available from Shin-Etsu Chemical Co., Ltd.)were mixed thereinto. The resultant mixture was homogeneously dispersedwith a high-speed rotation mixer and thereafter filtrated with acartridge filter (“SHP030” available from ROKI TECHNO CO., LTD.), thuspreparing a resin composition 5.

Preparation of Resin Composition 6

4 Parts of a bisphenol F type epoxy resin (“806L”, available fromMitsubishi Chemical Corporation, epoxy equivalent weight: about 185), 5parts of bixylenol type epoxy resin (“YX4000HK”, available fromMitsubishi Chemical Corporation, epoxy equivalent weight: about 185), 5parts of a naphthylene ether type epoxy resin (“EXA-7311-G4”, availablefrom DIC Corporation, epoxy equivalent weight: about 213), 15 parts of abiphenyl type epoxy resin (“NC3000L”, available from Nippon Kayaku Co.,Ltd., epoxy equivalent weight: about 272), 10 parts of a phenoxy resin(“YX7553BH30”, available from Mitsubishi Chemical Corporation, a 1:1solution of cyclohexanone:methyl ethyl ketone (MEK) having a solidcontent of 30% by mass), and 4 parts of a flame retardant (“PX-200”,available from DAIHACHI CHEMICAL INDUSTRY CO., LTD.) were heated anddissolved in a mixed solvent of 15 parts of solvent naphtha and 10 partsof cyclohexanone with stirring. After the resultant soliton was cooledto room temperature, 5 parts of a triazine skeleton-containing cresolnovolac-based curing agent (“LA3018-50P”, available from DICCorporation, hydroxyl equivalent weight: about 151, a 2-methoxypropanolsolution having a solid content of 50%), 15 parts of an activeester-based curing agent (“HPC-8000-65T”, available from DICCorporation, active group equivalent weight: about 225, a toluenesolution having a nonvolatile component of 65% by mass), 1.5 part of anamine-based curing accelerator (4-dimethylaminopyridine (DMAP), a MEKsolution having a solid content of 5% by mass), 110 parts of sphericalsilica (“ADMAFINE SO-C1”, available from Admatechs Company Limited,average particle diameter 0.63 μm, specific surface area 11.2 m²/g, truedensity 2.25 g/cm³, product of specific surface area and true density25.2 (m²/g·g/cm³), amount of carbon per unit surface area 0.35 mg/m²)surface-treated with an aminosilane-based coupling agent (“KBM573”available from Shin-Etsu Chemical Co., Ltd.) were mixed thereinto. Theresultant mixture was homogeneously dispersed with a high-speed rotationmixer and thereafter filtrated with a cartridge filter (“SHP030”available from ROKI TECHNO CO., LTD.), thus preparing a resincomposition 6.

The components used in the resin compositions 1 to 6 and the blendingamounts of the components (parts by mass of nonvolatile content) arelisted in the following table.

TABLE 1 Resin composition In terms of nonvolatile component 1 2 3 4 5 6Epoxy resin HP4032SS 0 4 0 0 4 0 YD-8125G 4 0 0 0 0 0 828EL 0 0 0 8 8 0806L 0 0 0 0 0 4 630LSD 0 0 4 0 0 0 NC3000L 18 0 15 18 0 15 YX4000HK 6 05 0 0 5 YL7760 6 0 0 6 0 0 EXA7311-G4 0 8 5 0 0 5 ESN-475V 0 15 0 0 15 0Curing agent HPC8000 0 3.9 9.75 0 0 9.75 LA3018 0 0 2.5 0 0 2.5 LA7052 60 0 6 0 0 SN-495V 7.2 0 0 7.2 0 0 BA-230S 0 13.5 0 0 13.5 0 ULL-950S 07.5 0 0 7.5 0 V-03 5 0 0 0 0 0 BURNOCK D-500 0 0 0 3.25 3.9 0 Inorganicfiller SPH516-05 110 90 110 0 0 0 SO-C1 0 0 0 0 90 0 SO-C1 0 0 0 110 0110 Phenoxy resin YX7553BH30 3 1.8 3 3 1.8 3 Curing accelerator DMAP0.05 0.02 0.075 0.05 0.02 0.075 Co(III) 0 0.03 0 0 0.03 0 Flameretardant PX-200 0 0 0 0 0 4 HCA-HQ 0 0 2 0 0 0 Rubber particle AC-3401N2 0 0 0 0 0 AC-3355 0 0 0 6 0 0 Total 167.25 143.75 156.325 167.5 143.75158.325

Preparation of Resin Sheet of Examples 1-1 to 1-3 and Examples 2-1 to2-3 and Resin Sheet of Comparative Examples 1-1 to 1-3 and ComparativeExamples 2-1 to 2-3

As a support, a PET film (“Lumilar R80”, available from TorayIndustries, Inc., thickness 38 μm, softening point 130° C., “releasePET”) subjected to release treatment with an alkyd resin-based releasingagent (“AL-5” available from Lintec Corporation) was prepared.

Each of the resin compositions was uniformly applied onto the releasePET with a die coater so that a thickness of resin composition layerafter drying was 13 μm. The applied resin composition was dried at 70°C. to 95° C. for 2 minutes to form a resin composition layer on therelease PET. Subsequently, a polypropylene film (“ALFAN MA-411”,available from Oji F-Tex Co., Ltd., thickness 15 μm) as a protectionfilm was laminated onto a surface of the resin composition layer thatwas not in contact with the support so that a rough surface of theprotection film was in contact with the resin composition layer. Thus, aresin sheet including the support, the resin composition layer and theprotection film in this order was obtained.

Separately, a resin sheet including the support, the resin compositionlayer having a thickness of 10 μm and the protection film in this orderwas prepared in a similar manner except that each resin composition wasuniformly coated on the release PET with a die coater so that athickness of the resin composition layer after drying was 10 μm.

Evaluation Test Measurement of Lowest Melt Viscosity

For the resin sheets of Examples 1-1 to 1-3 and Examples 2-1 to 2-3 andthe resin sheets of Comparative Examples 1-1 to 1-3 and ComparativeExamples 2-1 to 2-3, the lowest melt viscosity was measured by thefollowing method.

For the resin sheet including the resin composition layer having athickness of 13 μm, only the resin composition layer was peeled off fromthe release PET (the support). The resultant resin composition layer wascompressed with a mold, thus obtaining pellets for measurement (diameter18 mm, 1.2 g to 1.3 g).

The lowest melt viscosities (poise) were calculated by measuring adynamic viscoelasticity with a dynamic viscoelasticity measuringapparatus (“Rheosol-G3000” manufactured by UBM Co., Ltd.). For 1 g ofthe sample resin composition layer, the dynamic viscoelasticity wasmeasured using a parallel plate having a diameter of 18 mm underconditions of a measurement temperature range of 60° C. onset to 200°C., a temperature rise rate of 5° C./min, a measurement temperatureinterval of 2.5° C., a frequency of 1 Hz, and a strain of 1 deg. Theresults are listed in Table 2 and Table 3.

Measurement of Glass Transition Temperature of Cured Product (Examples1-1 to 1-3 and Comparative Examples 1-1 to 1-3)

The glass transition temperatures of the cured products of the resincomposition layers of the resin sheets of Examples 1-1 to 1-3 andComparative Examples 1-1 to 1-3 were measured by the following methods.A release PET film (“501010”, available from Lintec Corporation,thickness 38 μm, 240 mm square) was placed on a double-sided copper cladlayered body with an epoxy resin-glass cloth base material (“R5715ES”,available from Matsushita Electric Works, Ltd., thickness 0.7 mm, 255 mmsquare) so that an untreated surface of the release PET film was incontact with the double-sided copper clad layered body. Then, four sidesof the release PET film were fixed with a polyimide adhesive tape (width10 mm).

Each of the resin sheets (200 mm square) including the resin compositionlayer having a thickness of 13 μm prepared in Examples and ComparativeExamples was laminated onto the center of the release PET film(“501010”, available from Lintec Corporation) so that the resincomposition layer thereof was in contact with the release surface of therelease PET film using a batch type vacuum pressure laminator (CVP700,manufactured by Nikko Materials Co., Ltd., a two stage build-uplaminator). The lamination treatment was carried out by reducing thepressure for 30 seconds to an air pressure of 13 hPa or less and thenpressing for 30 seconds at 100° C. and a pressure of 0.74 MPa.

Subsequently, the board was thermally cured for 30 minutes under atemperature condition of 100° C. after placing the board in an oven at100° C., and then, for 30 minutes under a temperature condition of 175°C. after transferring the board to an oven at 175° C. Thereafter, theboard was taken out under a room temperature atmosphere and the releasePET (the support) was peeled off from the resin sheet. Thereafter, theboard was further thermally cured for 90 minutes under the curingconditions after placing the board in an oven at 190° C.

After thermal curing, the polyimide adhesive tape was peeled off and thecured product was removed from the double-sided copper clad layered bodywith an epoxy resin-glass cloth base material. Further, the release PETfilm (“501010” available from Lintec Corporation) on which the resincomposition layer was laminated was peeled off, thus obtaining asheet-like cured product. The obtained cured product is referred to as a“cured product for evaluation”.

A specimen having a width of about 7 mm and a length of about 40 mm wascut from the “cured product for evaluation” and subjected to dynamicmechanical analysis (DMA) in a tensile mode using a dynamic mechanicalanalyzer DMS-6100 (manufactured by Seiko Instruments Inc.). Thismeasurement was carried out in a range of 25° C. to 240° C. attemperature rise of 2° C./min and a frequency of 1 Hz. The glasstransition temperature (° C.) was determined to be a value obtained byrounding off the first decimal place of the maximum value of losstangent (tan δ) obtained by the ratio of storage elastic modulus (E′)and loss elastic modulus (E″). The results are listed in Table 2.

Measurement of extracted water conductivity of cured product (Examples1-1 to 1-3 and Comparative Examples 1-1 to 1-3)

The “cured product for evaluation” prepared in the section of“Measurement of glass transition temperature of cured prod” waspulverized using a pulverizer (PM-2005m, manufactured by Osaka ChemicalCo., Ltd.) and the pulverized material was sieved. 2.0 g of the fractionpassed through 150 μm and not passed through 75 μm was placed in apressure-resistant container with 40 g of ultrapure water and thepressure-resistant container was sealed tightly. A sample prepared byplacing 50 g of ultrapure water in a similar container and tightlysealing the container was used as a blank. The extraction conditionswere determined to be 120° C. for 20 hours or 160° C. for 20 hours.After the extraction, the container was quickly cooled with ice waterand the extracted suspension water was filtered through a membranefilter (MILLEX-GV, 0.22 μm, available from Merck Millipore Corporation).The electrical conductivity of each extracted water after filtration wasmeasured together with the blank. The extracted water conductivitieswere calculated from the following calculation formula. The results arelisted in Table 2.

Extracted water Conductivity (μS/cm)=Conductivity of extractedwater−Conductivity of blank.

Measurement of Tensile Breaking Strength of Cured Product (Examples 2-1to 2-3 and Comparative Examples 2-1 to 2-3)

The tensile breaking strengths of the cured products of the resin sheetsof Examples 2-1 to 2-3 and the resin sheets of Comparative Examples 2-1to 2-3 were measured by the following method.

A release PET film (“501010” available from Lintec Corporation,thickness 38 μm, 240 mm square) was placed on a double-sided copper cladlayered body with an epoxy resin-glass cloth base material (“R5715ES”available from Matsushita Electric Works, Ltd., thickness 0.7 mm, 255 mmsquare) so that an untreated surface of the release PET film was incontact with the double-sided copper clad layered body. Then, four sidesof the release PET film were fixed with a polyimide adhesive tape (width10 mm).

Each of the resin sheets (200 mm square) including the resin compositionlayer having a thickness of 10 μm prepared in the Examples andComparative Examples was laminated onto the center of the release PETfilm“501010”, available from Lintec Corporation) so that the resincomposition layer thereof was in contact with the release surface of therelease PET film using a batch type vacuum pressure laminator (CVP 700,a two stage build-up laminator, manufactured by Nikko Materials Co.,Ltd.) The lamination treatment was carried out by reducing the pressurefor 30 seconds to an air pressure of 13 hPa or less and then pressingfor 30 seconds at 100° C. and a pressure of 0.74 MPa.

Subsequently, the board was thermally cured for 30 minutes under atemperature condition of 100° C. after placing the board in an oven at100° C., an then for 30 minutes under a temperature condition of 175° C.after transferring to an oven at 175° C. Thereafter, the board was takenout under a room temperature atmosphere and the release PET (support)was peeled off from the resin sheet. Thereafter, the board was furtherthermally cured for 90 minutes under the curing conditions after placingthe board in an oven at 190° C.

After thermal curing, the sample to be subjected to a HAST test (HighlyAccelerated temperature and humidity Stress Test) was heated, as it was,at 130° C. for 100 hours under the condition of a relative humidity of85% using a highly accelerated life test apparatus (“PM422” manufacturedby ETAC Engineering Co., Ltd.). Thereafter, the polyimide adhesive tapewas peeled off and the cured product was removed from the double-sidedcopper clad layered body with an epoxy resin-glass cloth base material.Further, the release PET film (“50101”” available from LintecCorporation) on which the resin composition layer was laminated waspeeled off, thus obtaining a sheet-like cured product after the HASTtest having a thickness of 10 μm. For the sample not subjected to theHAST test, after thermal curing, the polyimide adhesive tape was peeledoff and the cured product was removed from the double-sided copper cladlayered body with an epoxy resin-glass cloth base material. Further, therelease PET film on which the resin composition layer was laminated waspeeled off, thus obtaining a sheet-like cured product having a thicknessof 10 μm. Among the thus obtained cured products, the sample notsubjected to the HAST test after curing are referred to as a “curedproduct A for evaluation”, and the samples subjected to the HAST testafter curing are referred to as a “cured product B for evaluation”.

Each of the “cured product A for evaluation” and the “cured product Bfor evaluation” was cut out into a dumbbell shape to obtain testspecimens. For test specimens, the tensile strength was measured inaccordance with JIS K 7127 using a tensile testing machine RTC-1250Amanufactured by Orientec Co., Ltd. to determine the tensile breakingstrength (MPa) at 23° C. The measurement was carried out on fivesamples, and the average values of the top three values are listed inTable 3. In Table 3, “Tensile breaking strength A of cured product”represents the tensile breaking strength (MPa) of the cured product Afor evaluation and “Tensile breaking strength B of cured product afterHAST test” represents the tensile breaking strength (MPa) of the curedproduct B for evaluation, and “B/A” represents the ratio of “Tensilebreaking strength B/Tensile breaking strength A”.

Evaluation of Insulation Reliability and Measurement of Thickness ofInsulating Layer Between Conductive Layers

Evaluation test on insulation reliability and measurement of thethickness of insulating layer between conductive layers for the resinsheets of Examples 1-1 to 1-3 and Examples 2-1 to 2-3 and the resinsheets of Comparative Examples 1-1 to 1-3 and Comparative Examples 2-1to 2-3 were carried out by the following method.

Preparation of Board for Evaluation (1) Substrate Treatment of InternalLayer Circuit Substrate

As an internal layer circuit substrate, a double-sided copper cladlayered body with an epoxy resin-glass cloth base material (“R1515F”,available from Panasonic Corporation, thickness of copper foil 18 μm,thickness of substrate 0.3 mm) on both surfaces of which circuitconductors (copper) were formed with a wiring pattern of 1 mm squarelattices (residual copper ratio: 59%) was prepared. Roughening treatmentof both of copper surfaces of the internal layer circuit substrate wascarried out with “CZ8201” available from MEC Co., Ltd. (copper etchingamount: 0.5 μm)

(2) Lamination of Resin Sheet

Each of the resin sheets (including a resin composition layer having athickness of 13 μm) prepared in Examples and Comparative Examples waslaminated onto both surfaces of the internal layer circuit substratewith a batch type vacuum pressure laminator (2 stage build-up laminator,CVP700, manufactured by Nikko Materials Co., Ltd.) so that the resincomposition layer thereof was in contact with the internal layer circuitsubstrate. The lamination was carried out by reducing the pressure for30 seconds to an air pressure of 13 hPa or less and then pressing for 45seconds at 130° C. and a pressure of 0.74 MPa, followed by thermalpressing for 75 seconds at 120° C. and a pressure of 0.5 MPa.

(3) Thermal Curing of Resin Composition Layer

The internal layer circuit substrate having the resin sheet laminatedthereon was thermally cured for 30 minutes under a temperature conditionof 100° C. after placing the internal layer circuit substrate in an ovenat 100° C. and then for 30 minutes under a temperature condition of 175°C. after transferring the internal layer circuit substrate to an oven at175° C., thus forming the insulating layer.

(4) Formation of Via Hole

A via hole having a top diameter (70 μm) was formed in the insulatinglayer on the conductor having the lattice pattern with a CO₂ laserprocessing machine “605GTWIII(-P)” manufactured by Mitsubishi ElectricCorporation by irradiating with laser from above the insulating layerand the support. The insulating layer was irradiated with laser underirradiation conditions of a mask diameter of 2.5 mm, a pulse width of 16μs, an energy of 0.39 mJ/shot, and a number of shots of 2, using a burstmode (10 kHz).

(5) Step of Carrying Out Roughening Treatment

The support was peeled off from the circuit board in which the via holewas formed and the desmear treatment was carried out. As the desmeartreatment, the following wet desmear treatment was carried out.

Wet Desmear Treatment:

The insulating layer was immersed in a swelling liquid (“Swelling DipSecuriganth P”, an aqueous solution of diethylene glycol monobutyl etherand sodium hydroxide, available from Atotech Japan K. K.) at 60° C. for5 minutes, subsequently an oxidant solution (“Concentrate Compact CP”,an aqueous solution of potassium permanganate having a concentration ofabout 6% and sodium hydroxide having a concentration of about 4%,available from Atotech Japan K. K) at 80° C. for 10 minutes, and finallya neutralizing liquid (“Reduction Solution Securiganth P”, an aqueoussolution of sulfuric acid, available from Atotech Japan K. K) at 40° C.for 5 minutes, and thereafter dried at 80° C. for 15 minutes.

(6) Step of Forming Conductive Layer

(6-1) Electroless Plating Process

In order to form a conductive layer on a surface of the circuit board, aplating process including the following processes 1 to 6 (a copperplating process using a chemical solution available from Atotech JapanK. K.) was carried out to form the conductive layer.

1. Alkaline Cleaning (Cleaning of Surface of Insulating Layer Providedwith Via Hole and Charge Adjustment)

Trade name: Cleaning Cleaner Securiganth 902 (trade name) was used towash the circuit board at 60° C. for 5 minutes.

2. Soft Etching (Washing Inside Via Hole)

The resultant circuit board was treated with sulfuric acidic aqueoussolution of sodium peroxodisulfate at 30° C. for 1 minute.

3. Pre-Dip (Adjustment of Charge on Surface of Insulating Layer for PdApplication)

The resultant circuit board was treated with Pre. Dip Neoganth B (tradename) at room temperature for 1 minute.

4. Activator Application (Application of Pd to Surface of InsulatingLayer)

The resultant circuit board was treated with Activator Neoganth 834(trade name) at 35° C. for 5 minutes.

5. Reduction (Reduction of Pd Applied to Insulating Layer)

The resultant circuit board was treated with a mixed liquid of ReducerNeoganth WA (trade name) and Reducer Acceralator 810 mod. (trade name)at 30° C. for 5 minutes.

6. Electroless Copper Plating Process (Cu is Deposited on Surface (PdSurface) of Insulating Layer)

The resultant circuit board was treated with a mixed liquid of BasicSolution Printganth MSK-DK (trade name), Copper solution Printganth MSK(trade name), Stabilizer Printganth MSK-DK (trade name), and Reducer Cu(trade name) at 35° C. for 20 minutes. The thickness of the electrolesscopper plating layer formed was 0.8 μm.

(6-2) Electrolytic Plating Process

Subsequently, an electrolytic copper plating process was carried outusing a chemical solution available from Atotech Japan K. K under suchcondition that copper was filled in the via hole. Thereafter, as aresist pattern for patterning by etching, a conductive layer having aland and a conductor pattern of thickness of 10 μm was formed on asurface of the insulating layer using a land pattern of diameter of 1 mmthat was conducted to the via hole and a circular conductor pattern ofdiameter of 10 mm that was not connected to the lower layer conductor.Subsequently, annealing treatment was carried out at 190° C. for 90minutes. The obtained board was used as a board A for evaluation.

(7) Measurement of Thickness of Insulating Layer Between ConductiveLayers

A cross section of the board A for evaluation was observed using aFIB-SEM complex apparatus (“SMI3050SE” manufactured by SIINanotechnology Co., Ltd.). Specifically, a cross section in thedirection perpendicular to a surface of the conductive layer was cut outby FIB (Focused Ion Beam) and a thickness of the insulating layerbetween the conductive layers was measured from a cross-sectional SEMimage. For each sample, cross-sectional SEM images of randomly selectedfive sites were observed and the average value thereof was determined tobe a thickness of the insulating layer between the conductive layers.The results are listed in Tables 2 and 3.

(8) Evaluation of Insulation Reliability of Insulating Layer

The board A for evaluation obtained above was conditioned using a highlyaccelerated life test apparatus (“PM422”, manufactured by ETACEngineering Co., Ltd.) for 200 hours under the condition of 130° C., arelative humidity of 85% and a DC voltage application of 3.3 V. Theinsulation resistance value of the board A for evaluation afterconditioned was measured using an electrochemical migration tester(“ECM-100”, manufactured by J-RAS Co., Ltd.) (n=6). In the measurement,a side of the circular conductor of diameter of 10 mm in the board A forevaluation obtained above was defined as a positive electrode and a sideof the lattice conductor (copper) of the internal layer circuitsubstrate connected to the land of diameter of 1 mm was defined as anegative electrode. The case where all of the six test specimens had theinsulation resistance values of 10⁷Ω or more was determined to be goodto be marked with a symbol of “+,” whereas the case where even one testspecimen had an insulation resistance value of less than 10⁷Ω wasdetermined to be problematic to be marked with a symbol of “−.” Theevaluation results are listed in Table 2 and Table 3. The insulationresistance values listed in Table 2 and Table 3 are the minimum valuesof the insulation resistance values of the six test specimens.

TABLE 2 Example Comparative Example 1-1 1-2 1-3 1-1 1-2 1-3 Resincomposition 1 2 3 4 5 6 Lowest melt viscosity of resin composition layer(poise) 2900 2400 3600 3300 3100 2300 Extracted water conductivity ofcured product 120° C. × 20 h (μs/cm) 33 47 35 63 56 45 Extracted waterconductivity of cured product 160° C. × 20 h (μS/cm) 91 170 140 240 190220 Glass transition temperature of cured product (° C.) 180 191 162 172186 151 Thickness of insulating layer between conductive layers (μm) 5.05.1 5.4 5.1 4.9 5.3 Evaluation of insulation reliability Insulationresistance value (Ω) 3.23 × 10⁸ 6.66 × 10⁹ 5.83 × 10¹⁰ 2.26 × 10² 3.46 ×10⁴ 5.00 × 10³ Evaluation result + + + − − −

TABLE 3 Example Comparative Example 2-1 2-2 2-3 2-1 2-2 2-3 Resincomposition 1 2 3 4 5 6 Lowest melt viscosity of resin composition layer(poise) 2900 2400 3600 3300 3100 2300 Tensile breaking strength A ofcured product (MPa) 88 81 77 75 80 73 Tensile breaking strength B ofcured product after HAST test (MPa) 71 59 60 44 39 46 B/A 0.81 0.73 0.780.59 0.49 0.63 Thickness of insulating layer between conductive layers(μm) 5.0 5.1 5.4 5.1 4.9 5.3 Evaluation of insulation reliabilityInsulation resistance value (Ω) 3.23 × 10⁸ 6.66 × 10⁹ 5.83 × 10¹⁰ 2.26 ×10² 3.46 × 10⁴ 5.00 × 10³ Evaluation result + + + − − −

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

As used herein the words “a” and “an” and the like carry the meaning of“one or more.”

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

All patents and other references mentioned above are incorporated infull herein by this reference, the same as if set forth at length.

1. A resin sheet, comprising: a support; and a resin composition layerbeing in contact on the support, wherein an extracted water conductivityA of a cured product of the resin composition layer when extracted at120° C. for 20 hours is 50 μS/cm or less and an extracted waterconductivity B of the cured product of the resin composition layer whenextracted at 160° C. for 20 hours is 200 μS/cm or less.
 2. The resinsheet according to claim 1, wherein a glass transition temperature of acured product of the resin composition layer is 160° C. or more.
 3. Aresin sheet, comprising: a support; and a resin composition layer beingin contact on the support, wherein a ratio (B/A) of a tensile breakingstrength B of a 10 μm thickness cured product of the resin compositionlayer after a HAST test to a tensile breaking strength A of a 10 μmthickness cured product of the resin composition layer is 0.65 or moreand 1 or less.
 4. The resin sheet according to claim 3, wherein thetensile breaking strength B is 50 MPa or more.
 5. The resin sheetaccording to claim 1, wherein said resin composition layer has athickness of 15 μm or less.
 6. The resin sheet according to claim 1,wherein said resin composition layer has a lowest melt viscosity of 1000poise or more.
 7. The resin sheet according to claim 1, wherein saidresin composition layer comprises an epoxy resin and a curing agent. 8.The resin sheet according to claim 1, wherein said resin compositionlayer comprises an inorganic filler in an amount of 50% by mass or morewhen a nonvolatile component in said resin composition layer isdetermined to be 100% by mass.
 9. The resin sheet according to claim 8,wherein the inorganic filler has an average particle diameter of 0.05 μmto 0.35 μm.
 10. The resin sheet according to claim 8, wherein a productof a specific surface area, in m²/g, and a true density, in g/cm³, ofthe inorganic filler is 0.1 to
 77. 11. An insulating layer of a printedwiring board, prepared by curing a resin sheet according to claim
 1. 12.The insulating layer according to claim 11, wherein said insulatinglayer is contained in a printed wiring board comprising a firstconductive layer and a second conductive layer, and said insulatinglayer insulates said first conductive layer from said second conductivelayer and has a thickness of 6 μm or less between said first conductivelayer and said second conductive layer.
 13. A printed wiring board,comprising: a first conductive layer, a second conductive layer, and aninsulating layer that insulates said first conductive layer from saidsecond conductive layer and has a thickness of 6 μm or less between saidfirst conductive layer and said second conductive layer, wherein saidinsulating layer is a cured product of said resin composition layer of aresin sheet according to claim
 1. 14. A semiconductor device, comprisinga printed wiring board according to claim
 13. 15. The resin sheetaccording to claim 3, wherein said resin composition layer has athickness of 15 μm or less.
 16. The resin sheet according to claim 3,wherein said resin composition layer has a lowest melt viscosity of 1000poise or more.
 17. The resin sheet according to claim 3, wherein saidresin composition layer contains an epoxy resin and a curing agent. 18.The resin sheet according to claim 3, wherein said resin compositionlayer contains an inorganic filler in an amount of 50% by mass or morewhen a nonvolatile component in said resin composition layer isdetermined to be 100% by mass.
 19. The resin sheet according to claim18, wherein said inorganic filler has an average particle diameter of0.05 μm to 0.35 μm.
 20. The resin sheet according to claim 18, wherein aproduct of a specific surface area, in m²/g, and a true density, ing/cm³, of the inorganic filler is 0.1 to
 77. 21. An insulating layer ofa printed wiring board, prepared by curing a resin sheet according toclaim
 3. 22. The insulating layer according to claim 21, wherein saidinsulating layer is contained in a printed wiring board comprising afirst conductive layer and a second conductive layer, and saidinsulating layer insulates said first conductive layer from said secondconductive layer and has a thickness of 6 μm or less between said firstconductive layer and said second conductive layer.
 23. A printed wiringboard, comprising: a first conductive layer, a second conductive layer,and an insulating layer that insulates said first conductive layer fromsaid second conductive layer and has a thickness of 6 μm or less betweensaid first conductive layer and said second conductive layer, whereinsaid insulating layer is a cured product of the resin composition layerof a resin sheet according to claim
 3. 24. A semiconductor device,comprising the printed wiring board according to claim 23.